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How would you refactor this JS function?

Lars Grammel on October 18, 2021

During the weekend, I found the following small JS function in a blog post: const lineChecker = (line, isFirstLine) => { let document = ``;...

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Keff • Oct 18 '21

Interesting function. I would need to have a closer look at the rest of the code to see whether refactoring this specific function is really the best option. It's seems like a weird function to me, and it does a few things.

The most straight forwards refactor would be:

const lineChecker = (line = '', isFirstLine = false) => {
    const hasLine = line !== '';
    if (!hasLine) return '<br />';

    return isFirstLine
        ? `<h1>${line}</h1>`
        : `<p>${line}</p>`;
};

But I don't know if line could be null or other falsy values as well, and if those would also return <br /> or not. In case we want to check for null values too:

const lineChecker = (line = '', isFirstLine = false) => {
    const hasLine = line !== '' && line != null;
    if (!hasLine) return '<br />';

    return isFirstLine
        ? `<h1>${line}</h1>`
        : `<p>${line}</p>`;
};

If it was me, I would prefer separating logic into separate functions to separate concerns. A function to check whether the line is empty or not, another one to get the line, one to generate the header, etc... something like that.

This is the initial idea that comes to mind:

const isEmpty = (line) => line !== '' && line != null;
const isFirstLine = (index) => index === 0;
const header = (line) => `<h1>${line}</h1>`;
const paragraph = (line) => `<p>${line}</p>`;
const br = () => `<br/>`;

const lineChecker = (line = '', index) => {
    if (isEmpty(line)) return br();

    return isFirstLine(index) 
        ? header(line) 
        : paragraph(line);
}

const checkLines = (lines = []) => lines.map(lineChecker);

Note that I have separated it into smaller more composable functions for better reusability. It's a longer solution, but I feel like it makes it quite a lot more extendable and reusable across the rest of the codebase.

This could be taken in multiple ways though, so this is just my take!

Lars Grammel • Oct 18 '21

Love it!

I'm a fan of simplicity so I ended up with the first solution you proposed (plus inlined hasLine), but I very much agree on your thoughts regarding null / undefined being passed in.

For your 3rd solution I was wondering where the line towards overengineering is, I think it depends very much on the project and it's context.

Full Name • Oct 18 '21

"It depends" definitely strikes me as the answer to the overengineering question.

Extracting predicates feels to me like an easy sell. Their reusability and the readability improvement approaches self evident. How many general purpose js libraries come without an isEmpty function?

The html strings would require more context (and pose more questions - what situation are we in that this is preferable to a robust templating solution?). Either Keff didn't mention it or I overlooked it, but the separate functions also permit independent testing.

Lars Grammel • Oct 18 '21 • Edited

In this particular example, I would consider extracting predicates premature abstraction. You might never need them, and you add unnecessary cognitive complexity. When it comes to testing, the function can easily be unit tested as is.

That being said, I am in favor of extracting predicates etc. when there is reuse and value in doing so, i.e. following the 3 strikes rule for refactoring.

Full Name • Oct 18 '21 • Edited

What added cognitive complexity is there in reading isEmpty rather than parsing the expression line !== '' && line != null?

WRT to testing, a mistake in a predicate would cause a test of that branch's eventual value to fail. Not because the code that produces that value is wrong, but because the predicate is wrong. Yes, you can still test every one of the diverse things this function is doing, but conflating multiple behaviors just makes finding the specific problem harder. It's changing 'the problem is here' to 'the problem is in this general area'.

Lars Grammel • Oct 18 '21 • Edited

The complexity is in the number of lines to read and in the links that you need to follow. The individual pieces might be simpler, but their sum is not due to their links. E.g. if you want to understand what paragraph does, you need to find and read the definition, keep it in your head, go back to the place where it was used, and then put it together.

Re testing, I agree that it's good to tear things apart (and introduce e.g. predicates), but only when the code is complex enought. I consider this method way too trivial to do that - it's far easier to test as one.

Full Name • Oct 18 '21 • Edited

Okay, I follow what you mean by complexity. Thank you for clarifying. I don't wish to say I disagree, but I don't think I share your perspective.

I think there's an argument to be made in the very particular case that a function (eg isEmpty) has a name (or function signature, or instantly visible documentation if one has the convenience of IDE like features) that is clear to the reader, and that function is separately tested. That it's separately tested allows me to trust that the implementation does what it should. That the name or signature (particularly the signature, tbh) accurately describe behavior allows me ignore implementation details when I'm reading lineChecker.

If my units (ie functions as the unit of composition) are well named and tested, I should be able to compose them without repeatedly diving into every implementation of every unit. If one can't do that, I think there is a massive problem in one's approach to writing and testing software.

Diving into every implementation detail of every function while reading to understand the behavior of a function/module/unit/etc strikes me as a premature step in a manner similar to what you've expressed about extracting things before there are demonstrated instances of reuse.

Edit to add: If one has to jump back to the implementation of every unit within their own code, Im not sure I see how one can logically avoid doing the same thing with library code. Does the average React user feel the need to read the implementation of useState, for example? If not, why is that function call privileged?

Lars Grammel • Oct 18 '21

Overall I think I agree with you and would have made similar arguments in the past. I often split code along similar lines in my projects, maybe with slightly different thresholds to method/function extraction.

However it seems to assume a perfect world with perfect software development projects, or that you and only you own the code, and you never need to hand it over to someone else.

In the reality that I've encountered in professional life, time pressure, employee turnover, mistakes, and other forces lead to source code being far from perfect, sadly. Trusting the function name or that a function is sufficiently tested is a bet in that world. I would not call that "a massive problem in one's approach" - for one-person projects, it's not an issue at all. It happens when shifting teams of developers work on moving requirements over multiple years, and it's non-trivial to avoid.

In that world, I prefer going for code that's as simple and predictable as possible, and that's why I prefer not extracting functions or predicates unless it is genuinely needed (either for testing or because it reduces code complexity, e.g., by removing duplication).

Thanks for the long reply; I enjoyed hearing your perspective!

Full Name • Oct 18 '21

Fair enough.

Professionally I've encountered sprawling monoliths with no tests at all and team leads who felt it was okay because it had been in production longer than I had been with the company. Your quite right, none of us can avoid reality. It does not, however, change what I would aim for or advise to others.

Likewise, thank you for the civil discussion!

Keff • Oct 18 '21

Great point on overengineering, I must admit the last solution could be a bit overengineered. That's the reason I would need to check the full code base and see the real use of this function.

I too prefer simplicity in general, so I would probably go for the first example.

Keff • Oct 18 '21

On the point of the hasLine variable, it's just my personal preference, I really like how readable it makes the conditions.

Lars Grammel • Oct 18 '21

It definitely makes the code more understandable.

RRKallan • Oct 19 '21

There is a small bug in your last solution

const isEmpty = (line) => line !== '' && line != null;

returns false when line = "" and true when line = "test"

possible solution

const isEmpty = (line) => !line && line !== 0;
const isFirstLine = (index) => !index;
const getElementTag = (index) => (isFirstLine(index) ? "h1" : "p");
const getText = (line, index) => {
    const elementTag = getElementTag(index);
    const text = `<${elementTag}>${line}</${elementTag}>`;
    return text;
};
const br = () => "<br />";
const lineChecker = (line = "", index) => {
    if (isEmpty(line)) return br();

    return getText(line, index);
};

const checkLines = (lines = []) => lines.map(lineChecker);

Keff • Oct 19 '21

Ohh my bad. Thanks for pointing it out! I did not run the code after the refactor (big mistake when refactoring)

RRKallan • Oct 19 '21

haha can happen :)

Keff • Oct 19 '21

It definitely does, I've been away from javascript for a while, mostly working with dart/flutter...

Hanan Hamza • Oct 19 '21

the easiest way to check for all falsy values would be if(!!line === false)

RRKallan • Oct 19 '21

What do you think about?

If(!line)

Siddharth • Oct 18 '21

To check for non-nullish I'd suggest using ??.

Calin Baenen • Oct 18 '21

I love your refactor. So simple!

Spyros Argalias • Oct 19 '21 • Edited

Solution to this question

For this particular function, I would just remove the unnecessary conditionals. I wouldn't turn it into a one-liner. I also wouldn't give it more complicated logic than simple if statements.

const lineToHtml = (line, isFirstLine) => {
  if (typeof line !== 'string') {
    return '';
  }
  if (line === '') {
    return '<br>';
  }
  if (isFirstLine) {
    return `<h1>${line}</h1>`;
  }
  return `<p>${line}</p>`;
};

The real problem

However, passing a Boolean into a function is considered a code smell. Some downsides are that:

it's a strong indication that the function is doing multiple things. This one is doing 4 things.
it makes it more difficult to test (because of the number of code paths).
it's more troublesome to reuse it. Some other code in the codebase may want to surround something with h1 tags, without caring about the other cases. But, instead of calling something like createHeading(text), it needs to bother with more parameters and call lineToHtml(text, true)
it doesn't grow well. As you need more formatting functionality in the future, you'll modify this function, give it more logic, and more parameters.

The real solution

The solution is to refactor the parent of this function to something like this:

const parent = (textLines) => {
  return textLines.map((line, i) => {
    if (i === 0) {
      return toHtmlHeading(line);
    }
    return toHtmlParagraph(line);
  })
}

Then, make the lower-level functions only do one thing:

const toHtmlHeading = (text) => `<h1>${text}</h1>`;
const toHtmlParagraph = (text) => `<p>${text}</p>`;

RRKallan • Oct 20 '21 • Edited

a H1 could be used multiple times, there fore it could be line 3, 9, 18 etc etc. So to check and set it only on first iteration, is from my perspective not correct

Also in the provided solution the <br /> is missing and would there placed a empty <h1> on first iteration and for all other <p>

Spyros Argalias • Oct 20 '21 • Edited

The solution was just an example of how you can remove the Boolean argument for better code overall. It's just a fictional example.

Depending on what you need, you could make changes. For example, you can add a function for the <br> just like toHtmlHeading, or you could have a function such as toHtmlElement(text, tag) instead of individual functions for each element, or you could have a completely different parent.

Edit: Replaced my answer to also answer the added second part.

RRKallan • Oct 20 '21

so based on the original provided code there is no iteration.
And on that function variable name is isFirstLine as boolean. And then just be an ashole, but isFirstLine could refer to new section

Spyros Argalias • Oct 20 '21

I know there's no iteration in the original example. In my answer I'm making a guess at what a caller of lineChecker might intend to do. It's not shown in the opening post. I'm just creating it myself. It's fictional, so it won't always apply.

Sure, isFirstLine could refer to whatever you want. Anyone can name anything what they want. If, in your application, that could refer to a new section, then my example solution wouldn't apply.

Sorry, I didn't quite catch that but did you mean to call me an "asshole" there, or am I misunderstanding?

RRKallan • Oct 20 '21

Sorry, I didn't quite catch that but did you mean to call me an "asshole" there, or am I misunderstanding?

No i'm not mentioning you, it meant to me because of the question. There I totally can understand your approach

Spyros Argalias • Oct 20 '21

I see, sorry for asking and for misunderstanding.

Good points :)

RRKallan • Oct 20 '21

No sorry please. Always better to ask and to clarify.
Also good to see and hear different approaches.

Which also is good that you can defend and clarify your solution.

Kimmo Sääskilahti • Oct 20 '21

Excellent answer, I like that you got rid of the boolean argument.

Now I'm only waiting for someone to write unit tests, in my world those are written before refactoring :)

RRKallan • Oct 20 '21

it("should handle parent", () => {
    const textLinesAsArray = ["line 1", "line 2", "", "line 4"];

    const expectedValue = ["<h1>line 1</h1>", "<p>line 2</p>", "<p></p>", "<p>line 2=4</p>"];
    const resultValue = parent(textLinesAsArray);

    expect(resultValue).toEqual(expect.arrayContaining(expectedValue));
    expect(expectedValue).toEqual(expect.arrayContaining(resultValue));
    expect(resultValue.length).toEqual(expectedValue.length);
});

it("should handle toHtmlHeading", () => {
    const value = "Heading title";

    const expectedValue = "<h1>Heading title</h1>";
    const resultValue = toHtmlHeading(value);

    expect(resultValue).toEqual(expectedValue);
});

it("should handle toHtmlParagraph", () => {
    const value = "Paragraph text";

    const expectedValue = "<p>Paragraph text</p>";
    const resultValue = toHtmlParagraph(value);

    expect(resultValue).toEqual(expectedValue);
});

didnt test these but i think this would be a start for testing.

And it's a choice TDD or BDD. It all depends on application. preferred working approach,
And in this case the question is to refactor the code. Basically there would be no need to change the tests. Still you will insert same input and would expect the same output

Except 2 or 3 solutions added new functions. So only on that case you would write new test

Spyros Argalias • Oct 20 '21

Good suggestion :)

Austin Shelby • Oct 18 '21

I would first start thinking about what this function actually does.

For me the name lineChecker is a little bit misleading because it looks like the function actually parses strings to html.

This is what I came up with:

const parseStringToHtml = (
  isFirstLine: boolean,
  line?: string
): string => {
  if (!line) {
    return "<br />";
  } else if (isFirstLine) {
    return `<h1>${line}</h1>`;
  } else {
    return `<p>${line}</p>`;
  }
};

For a function this small there isn't really much to refactor. Parsing markdown has been done thousands of times already and there are libraries that do this perfectly.

Cool puzzle nonetheless.

RRKallan • Oct 18 '21 • Edited

Adding the types makes sense.

Only the else if else statement could be replaced. My suggestion based on your example

const parseStringToHtml = (line = "", isFirstLine = false): string => {
    if (!line) return "<br />";

    if (isFirstLine) return `<h1>${line}</h1>`;

    return `<p>${line}</p>`;
};

edited

Siddharth • Oct 18 '21

I'd suggest putting the line argument in the function first, as line is more important and isFirstLine can have a default value

RRKallan • Oct 18 '21

true i just copy paste it and didn't read the arguments.

Lars Grammel • Oct 18 '21 • Edited

The renaming idea + introducing types is great!

To me, the method seems to be more of a print than a parse method (but I don't have the full context, just saw it in isolation).

James Thomson • Oct 19 '21

Extra bonus points for renaming the function. This would be my first improvement. Even if you left the function as is and just renamed it to describe its purpose that's a huge improvement in my book.

RRKallan • Oct 18 '21

Assumption:

line must is a string and length >= 1 return line
isFirstLine is a boolean true htmlTag = h1 else htmlTag = p

const lineChecker = (line = "", isFirstLine = false) => {
    if (typeof line !== "string" || !line.length) return "<br />";

    const elementTag = isFirstLine === true ? "h1" : "p";
    return `<${elementTag}>${line}</${elementTag}>`;
};

Lars Grammel • Oct 18 '21

Nice refactoring, I like the tag extraction and the input type checking!

RRKallan • Oct 18 '21

THX.

Ben Sinclair • Oct 19 '21 • Edited

I'd address two problems:

I don't know what this function does

lineChecker doesn't tell me what it's checking, or what a "line" is, for that matter. I can guess it's a single line from some text based on the contents of the function, but...

This function doesn't do what it says

This function returns a formatted string based on the current line. It's producing output, not checking something. I'd expect a "check" function to return some meta information or a boolean regarding the passed data's validity.

As far as refactoring goes, there's no point in defining the document variable at all, and its name is misleading - it's a single HTML element as a string. "Document" is a word we associate with the DOM or, well, entire documents.

The last else if is redundant, it's the same as an else there.

I'd probably do this, but I'm not overjoyed about it:


javascript
formatLineAsHtmlFragment(line, isFirstLine) {
  if (line === "") {
    return "<br>";
  }

  if (isFirstLine) {
    return `<h1>${line}</h1>`;
  }

  return `<p>${line}</p>`;
}

EDIT: why is my code not formatted as javascript when I did the backtick dance?

Lars Grammel • Oct 19 '21

Triple-backtick javascript worked for me to get JS formatting.

Ben Sinclair • Oct 20 '21

I just changed it to that and it still breaketh!

Lars Grammel • Oct 20 '21

javascript needs to be immediately after the 3 backticks, and needs to be followed by a newline.

Ben Sinclair • Oct 20 '21

It is, and it's exactly how I've done it in all my other posts where it works fine. I'm not sure what's wrong with this one. Anyway, people can imagine what it's like with colours :)

Siddharth • Oct 18 '21

Simplified one liner, with default props

const lineChecker = (line = '', isFirstLine = false) => line === '' ? '<br />' : `${isFirstLine ? `<h1>${line}</h1>` : `<p>${line}</p>`}`

Note that this isn't a very scalable solution. Scaling this will need a complete rewrite.

Siddharth • Oct 18 '21 • Edited

The bigger answer is "it depends". If this is it (which probably isn't), you can use my solution. If not there are many ways of making this extensible, like mapping conditions and tags in an array so we can simply add an item to the array to add more elements. Or we could refactor the wrapping in elements to a custom function. There are many more ways we can do this, I'm just mentioning the ones which come to mind

Calin Baenen • Oct 18 '21 • Edited

Rerefactor based on Keff's answer.

const lineChecker = (ln="", isLn1=false) => {
    ln = ln ?? ""; isLn1 = isLn1 ?? false;

    const empty = ln.length == 0;
    if(empty) return "<br/>";
    return isLn1 ? `<h1>${ln}</h1>` : `<p>${ln}</p>`;
};

Theoretically, this is the most optimized you can get.
BUT, if we use TypeScript, and go the mathematical route of only using one letter per var-name, we get this:

const c:Function = (l:string="", f:boolean=false) => {
    const e:boolean = ln.length == 0;
    if(e) return "<br/>";
    return f ? `<h1>${l}</h1>` : `<p>${l}</p>`;
};

Assuming people use the correct types in JS, as if we we're in a strongly typed language, we get the final result of:

const c = (l="", f=false) => {
    const e = l.length == 0;
    if(e) return "<br/>";
    return f ? `<h1>${l}</h1>` : `<p>${l}</p>`;
};

But, we can make e a one-time expression:

const c = (l="", f=false) => {
    if(l.length == 0) return "<br/>";
    return f ? `<h1>${l}</h1>` : `<p>${l}</p>`;
};

LOOK! It's a 2-liner! :O

However, (to me) this looks like the end of the road for refactorization, I don't think we can make this any smaller,- and if you can, it's because of a very niche detail.
But I think this is the best optimization from the original function.

RRKallan • Oct 19 '21 • Edited

understandable and readable is very hard in your solution.
Refactor is not to get code smaller.

I prefer === checks instead ==
I prefer !?.length instead l.length == 0

According to w3 guidelines, a space should be included before the trailing / and > of empty elements, for example, <br />. These guidelines are for XHTML documents to render on existing HTML user agents.

edited

Calin Baenen • Oct 19 '21 • Edited

understandable and readable is very hard in your solution.
Refactor is not to get code smaller.

Then I think the people who submitted those one-liners (Which are even harder to understand than my code!) misunderstood the point. :p

RRKallan • Oct 19 '21

the one line solutions with nested ternary expressions are also difficult to understand.

RRKallan • Oct 19 '21

Goals for refactoring code: readability, understandability, maintainability, performance, usage of latest code style / programming / functions / methods

Calin Baenen • Oct 19 '21

According to w3 guidelines, a space should be included before the trailing / and > of empty elements, for example,

I don't think your example works as intended.

Also, why is that? Does the space do something to make the HTML more understandable to some interpreters?

RRKallan • Oct 19 '21

edited my comment

Mark Holtzhausen • Oct 19 '21 • Edited

I came up with two revisions. The first is what I would actually prefer because of its readability. The second was just for fun.

const lineCheck = (line, isFirstLine) => {
  if(line==='') return '<br />'
  if(isFirstLine) return `<h1>${line}</h1>`
  return `<p>${line}</p>`
}

This is nice and readable -- and a trick I learned early on was to exit early if you have an simple condition that determines the outcome.

This one does the same, but more concise.

const lineCheckConcise = (line, isFirstLine)=>
  line !== ''
    ? (isFirstLine ? `<h1>${line}</h1>` :  `<p>${line}</p>`) 
    : '<br />'

The parentheses are not necessary, but makes it more readable. Also, I broke this into multiple lines to avoid horizontal scroll, but this is actually a single line function.

ReggieLee • Oct 18 '21

const lineChecker = (line, isFirstLine) => (`${line === "" ? <br /> : (isFirstLine ? `<h1>${line}</h1>` : `<p>${line}</p>`)}`)

I like the shortest way, but it seems is not readability

André Tissot • Oct 20 '21

I tend to prefer a balance between smaller and readable code:

const lineChecker = (line, isFirstLine) => {
  if(line === "") return "<br />";
  if(isFirstLine) return `<h1>${line}</h1>`;
  return `<p>${line}</p>`;
};

But as many things, this is just a personal preference, and the team conventions should always supersede.

𒎏Wii 🏳️‍⚧️ • Oct 19 '21

Other than shortening it a bit, I'd change the second parameter:

const lineChecker = (ilne, followup) =>   line
  ? followup
      ? `<p>${line}</p>`
      : `<h1>${line}</h1>`
   : `<br>`

Why switch the boolean around? Because now you can do

let liens = ["Title", "", "paragraph"].map(lineChecker)

Paweł Miczka • Oct 19 '21

function lineChecker(line: string, isFirstLine: boolean) {
    if (line === '') return '<br />';

    return {
        [0]: `<p>${line}</p>`,
        [1]: `<h1>${line}</h1>`
    }[Number(isFirstLine)]
}

but for that I would probably try to style it with CSS using ::first-line

Paweł Miczka • Oct 19 '21

it is possible to use array too

function lineChecker(line: string, isFirstLine: boolean) {
    if (line === '') return '<br />';

    return [
        `<p>${line}</p>`, 
        `<h1>${line}</h1>`
    ][Number(isFirstLine)];
}

Paweł Miczka • Oct 19 '21

and yet another idea - use markdown cause why not?

Valeria • Oct 19 '21

What about this one?

const lineChecker = (line, isFirstLine) => {
  if(!line?.trim()) return '<br/>'
  const tag = isFirstLine? 'h1':'p'
  return `<${tag}>${line}</${tag}>`
};
// Trim is needed to handle newlines & whitespaces
lineChecker('   \n   ',false) // <br/>

Vincent A. Cicirello • Oct 18 '21 • Edited

I didn't read through all of the other comments so someone else may have already suggested this one, but if the objective is to minimize conditions that are explicitly checked, start with the last case like this:

const lineChecker = (line, isFirstLine) => {
  if (line === "") {
    return "<br />";
  } else if (!line) {
    return ``;
  } else if (isFirstLine) {
    return `<h1>${line}</h1>`;
  } else {
    return `<p>${line}</p>`;
  } 
};

I also got rid of the concats with the unnecessary local variable.

James Thomson • Oct 19 '21

When using the early return method, you don't need else if. Just use if.

Utsav Ladani • Oct 19 '21

If line is plain text, then you should use object to add HTML in document instead of document += ....

const header = document.createElement("h1")
header.textContent = line
document.append(header)

It makes function faster

Andi Rosca • Oct 20 '21

My version:
I like to leave the happy path as the default return, and early return for any
exceptions

const lineChecker = (line, isFirstLine) => {
  if (!line) return "<br />";
  if (!isFirstLine) return `<p>${line}</p>`;
  return `<h1>${line}</h1>`;
};

jameslongstaff • Nov 8 '21

Personally I'd do..



const lineChecker = (line, isFirstLine) => {
  let document = "<br />";

  if (line.length) {
    const tag = isFirstLine ? 'h1' : 'p';
    document = `<${tag}>${line}</${tag}>`;
  }

  return document;
};

wrthfl • Oct 19 '21

My, maybe naive solution would be this:

const checkLines = (line = "", isFirstline = false) => {
  if (typeof line !== "string") return false;
  if (line === "") return "<br />";
  if (isFirstline) return `<h1>${line}</h1>`;
  else return `<p>${line}</p>`;
}

Not a fan of ternary operators, so i put it like this.
Would love to get feedback on this too since i am most certainly not a pro.

RRKallan • Oct 19 '21

Assumption when line is not a string return empty string or nothing. In that case there would be no need for a check to print the line. But as I said, it’s a assumption.

The else is redundant and could be replaced with the return statement.

panthablack • Oct 20 '21

The most pressing concern here (imo) is the function name - I don't know what it is meant to do, and certainly doesn't just 'check' lines - it constructs lines of HTML based on the arguments passed in and returns a string.

To refactor I would first look at the function in context and rename it something appropriate based on its intended use - the next steps would likely be as much to do with preferred style as anything else after that point. (Personally I lean towards declarative so I liked the solutions I have seen in the comments where the code was DRYed up using clearly named, reusable functions, but this is just personal preference.)

RRKallan • Nov 1 '21

you touching a good point about the function name.
But the case is refactor a peace of code.
Would you rename the function, or would you write a new function with the correct understandable name also for the param?

tq-bit • Oct 30 '21 • Edited

Leaving out all further context, this might be one of the rare occasions where to make use !! (double ! operator)

const lineChecker = (line = '', isFirstLine = false) => {
  if (!!line) {
    return isFirstLine ? `<h1>${line}</h1>` : `<p>${line}</p>`;
  }
  return '<br/>';
};

Note: After looking through some other solutions, I figured using !! introduces (or solves? I wouldn't know) a problem when passing unexpected falsy - values such as null, false or undefined.

I'd still say it's a pretty good example for refactoring. Even though it seems fairly easy to overengineer if you adhere to the 'functions do a single thing' mantra.

lucus-30 • Oct 23 '21

functional implementation with ramda

import { always, curry, ifElse, isEmpty, pipe, split, join, map }  from "ramda"

const html = curry((tagName, str) => `<${tagName}>${str}</${tagName}>`)
const h1 = html("h1")
const p = html("p")
const br = always("<br>")

const formatLines = map(ifElse(isEmpty, br, p))
const formatText = ([title, ...lines]) => [h1(title), ...formatLines(lines)]

const textToHTML = pipe(
  split("\n"),
  formatText,
  join("\n")
)

Derek Enos • Oct 22 '21

Here's my one-liner that includes a hilarious immediately-invoked arrow function:

const lineChecker = (line, isFirstLine) =>
      line === ""
      ? "<br />"
      : (tag => `<${tag}>${line}</${tag}>`)(isFirstLine ? "h1" : "p")

radotooo2 • Oct 22 '21

const lineChecker = (line, isFirstLine) => {
  const document = ``;

  if (line === "") return document.concat("<br />");

  isFirstLine ? document.concat(`<h1>${line}</h1>`) : document.concat(`<p>${line}</p>`);

  return document;
};

Ryan Kuruppu • Oct 21 '21

I'd have to see the rest of the code to decide whether or not this would be the best case but for now

const lineChecker = (line, isFirstLine) => {
    if(line !== "" && line != null)
        return isFirstLine ? `<h1>${line}</h1>` :  `<p>${line}</p>`;

    return "<br />";
}

Note that I've used != instead of !== in order to check for undefined. If you were going the strict approach you'd have used !== instead but because we're unaware of what will be coming in line. We're using a non-strict check here. I think this is a fairly simple solution in this case

machinesrental • Oct 21 '21 • Edited

"fat" version:

const lineChecker = (line, isFirstLine) => {
  if(typeof line !== 'string' || line === '') return '<br />';
  const tag = isFirstLine ? 'h1' : 'p';
  return `<${tag}>${line}</${tag}>;
}

minimal:

const lineChecker = (line, isFirstLine) => (typeof line !== 'string' || line === '') ? '<br />' : isFirstLine ? `<h1>${line}</h1>` : `<p>${line}</p>`

Vesa Piittinen • Oct 20 '21 • Edited

Well there are certainly more problems with this than just this function. For example we don't know if the line data has been escaped properly.

So if we go a bit outside the box of the function, and we keep the logic we could generate the document like this:

const document = text
  .trim()
  .split('\n')
  .map((line, index) =>
    (line === '' && '<br />') ||
    (index === 0 && `<h1>${line}</h1>`) ||
    `<p>${line}</p>`
  )
  .join('\n')

However this smells from HTML / CSS perspective because we're generating HTML like this:

<h1>Hello World</h1>
<br />
<p>Why there is a line break between paragraphs?</p>
<br />
<p>Did someone set paragraph margins to zero? That is evil business!</p>
<br />
<br />
<br />
<br />
<br />
<p>OMG I can do formatting with line breaks. Woohoo.</p>

While it works it is "ugly", and giving users the power to do as many line breaks as possible isn't often really desired. So we could only separate paragraphs when we have multiple line breaks in the source text.

const document = text
  .trim()
  // try this out at https://regex101.com
  .split(/\n\s*\n/)
  .map((line) => line.replace(/\n/g, '<br />'))
  .map((line, index) => index === 0 ? `<h1>${line}</h1>` : `<p>${line}</p>`)
  .join('\n')

And now we get "nicer" HTML output:

<h1>Hello world!</h1>
<p>I can no longer have multiple line breaks between paragraphs.</p>
<p>However I can...<br />now...<br />have...<br />line breaks...<br />within paragraphs! (And the header too.)</p>
<p>And paragraphs can retain their margins in CSS like they should when normal text is concerned.</p>

But this isn't good either, because this is still a non-standard way of parsing text to HTML. To have confidence you should make extensive tests to cover possible edge cases, and you have to maintain it yourself. So what to do?

Just use Markdown.

It might be worth the pain to refactor to using some Markdown library. Don't write your own, by now there are plenty of options that fit about any use case imaginable.

EECOLOR • Oct 20 '21

I don't like boolean parameters. Removing the boolean by splitting it into two functions makes is a lot more readable. At the call site you will know if it is the first line or not.

function formatFirstLine(line) {
  return line && `<h1>${line}</h1>`
}

function formatLine(line) {
  return line
    ? `<p>${line}</p>`
    : `<br />`
}

Please note that formatFirstLine assumes line is a string.

Júlio Gori Corradi • Oct 20 '21 • Edited

I was looking below and there are good examples very similar to what came to my mind but what I'm thinking right now is why anyone doesn't get bothered by the function name?!

The function is called lineChecker but the main responsibility is to return a well-formatted line.

So the main change that I can purpose here is to call it lineFormatter!

Peter Vivo • Oct 19 '21

I like ternary operator in arrow function, even multiple ternary. So I use this tabulation for clear reading. Work even lineChecker() , lineChecker([42],1) use cases too.

const lineChecker = (line, isHeader) => !line
  ? line === "" 
    ? "<br />"
    : ""
  :  isHeader
    ? `<h1>${line}</h1>` 
    : `<p>${line}</p>`
;

Peter Vivo • Oct 19 '21

Additional test cases, figure out without try it.

lineChecker([])
lineChecker(+[])
lineChecker(Infinity)

Chris Howard • Oct 22 '21

This is a simple as I could get it while retaining readability

const lineChecker = (line = "", isFirstLine = false ) => {
  let document = isFirstLine ? `<h1>${line}</h1>` : `<p>${line}</p>`
  return line ? document : `<br />`
}

Timothy Foster • Oct 19 '21 • Edited

The first thing I would do is change the name, perhaps to parseLineToHtml, which is more in line with what it does.

The second thing unfortunately depends on context, but the isFirstLine parameter bothers me. Probably because this function is very close to being able to operate on single lines independent of additional context, if not for that parameter.

The third thing is probably shuffle the br condition to be first so we don't have to repeatedly ask if the line isn't empty. Personally, I don't mind small, non-nested if-ladders as they can sometimes be more readable than ternaries.

And finally, I wouldn't do any of that without tests ( :

Calin Baenen • Oct 18 '21

Here's a good one:

const lineChecker = (line, isLn1) => {
    isLn1 = isLn1 ?? false; line = line ?? "";
    const nEmpty = line.length > 0;
    let doc = "";

    if(nEmpty && isLn1) doc += `<h1>${line}</h1>`;
    if(nEmpty && !isLn1) doc += `<p>${line}</p>`;
    if(!nEmpty) doc += "<br/>";

    return doc;
};

gustavoalias • Oct 18 '21

Another approach


const lineChecker = (line, isFirstLine) => {
  if(line!=='')
    {
      return isFirstLine ? `<h1>${line}</h1>` : `<p>${line}</p>`
    }
  else {
    return "<br />";
  }
};

Keff • Oct 19 '21

Great addition, I always like your functional approaches!!

rinahs • Oct 18 '21 • Edited

const lineChecker = (line, isFirstLine) => {
if (line !== '') {
if (isFirstLine) {
return <h1>${line}</h1>;
}
return <p>${line}</p>;
}
return <br />;
}

lynn • Oct 19 '21

I'd just rename it and call it lineFormatter, and add comments about sample inputs and outputs.

SenthilKumaranC • Oct 26 '21 • Edited

I have refactored like below. Divided all conditions to Spec Units and Grouped Spec Units. Check my Github Link to see my code.


const specApis = specificationGroup();

specApis.addSpecObject(headerSpecGroup, headerSpecGroupCallback);
specApis.addSpecObject(paragraphSpecGroup, paragraphSpecGroupCallback);
specApis.addSpecObject(isEmpty, breakSpecGroupCallback);

export const lineChecker = (line, isFirstLine) => {
    let initialDocument = "";
    return specApis.validateSpecs({ initialDocument, line, isFirstLine });
}

github.com/SenthilKumaranC/How-To-...

Sebastien Rodrigues • Oct 22 '21

const lineChecker = (Line,isFirstLine) =>
return line === « » ? «
» :
isFirsLine ? « H1 … » :

;

npc pratt • Oct 24 '21

One-liner:

const lineChecker = (line, isFirstLine) => line ? isFirstLine ? `<h1>${line}</h1>` : `<p>${line}</p>` : "<br />"

pbergwerff • Oct 19 '21

const lineChecker = (line, isFirstLine) => line !== "" ? isFirstLine ? `<h1>${line}</h1>` : `<p>${line}</p>` : `<br />`;