Blessing Hirwa

Posted on Jan 25, 2021 • Updated on Apr 27, 2021

17 Javascript optimization tips to know in 2021 🚀

#react #webdev #javascript #codenewbie

You might be using Javascript development for a long time but sometimes you might not be updated with newest beautiful features that it offers which can solve your issues without writing extra codes. These techniques can help you write clean and optimized JavaScript Code. Moreover, these topics can help you to prepare yourself for JavaScript interviews in 2021.

After one of my articles about 8 neat javascript skills you didn't know in 4 minutes, here I am coming with a new series to cover shorthand techniques that help you to write more clean and optimized JavaScript Code.My motive is to introduce all the JavaScript best practices such as shorthand and features which we must know as a frontend developer to make our life easier in 2021.This is a Cheat list for JavaScript Coding you must know in 2021.

1. If with multiple conditions

We can store multiple values in the array and we can use the array includes method.

//longhand
if (x === 'abc' || x === 'def' || x === 'ghi' || x ==='jkl') {
    //logic
}
//shorthand
if (['abc', 'def', 'ghi', 'jkl'].includes(x)) {
   //logic
}

2. If true … else Shorthand

This is a greater shortcut for when we have if-else conditions that do not contain bigger logics inside. We can simply use the ternary operators to achieve this shorthand.

// Longhand
let test= boolean;
if (x > 100) {
    test = true;
} else {
    test = false;
}
// Shorthand
let test = (x > 10) ? true : false;
//or we can simply use
let test = x > 10;
console.log(test);

After nesting the condition we remain with something which looks like this:

let x = 300,
let test2 = (x > 100) ? 'greater 100' : (x < 50) ? 'less 50' : 'between 50 and 100';
console.log(test2); // "greater than 100"

3. Null, Undefined, Empty Checks

When we do create new variables sometimes we want to check if the variable we are referencing for its value is not null or undefined. JavaScript does have a really good shorthand to achieve these functions.

// Longhand
if (first !== null || first !== undefined || first !== '') {
    let second = first;
}
// Shorthand
let second = first|| '';

4. Null Value checks and Assigning Default Value

let first = null,
let second = first || '';
console.log("null check", test2); // output will be ""

5. Undefined Value checks and Assigning Default Value

let first= undefined,
let second = first || '';
console.log("undefined check", test2); // output will be ""

6.foreach Loop Shorthand

This is a useful short hand for iteration

// Longhand
for (var i = 0; i < testData.length; i++)

// Shorthand
for (let i in testData) or  for (let i of testData)

Array for each variable

function testData(element, index, array) {
  console.log('test[' + index + '] = ' + element);
}

[11, 24, 32].forEach(testData);
// prints: test[0] = 11, test[1] = 24, test[2] = 32

7. Comparison returns

Using the comparison in the return statement will avoid our 5 lines of code and reduced them to 1 line.

// Longhand
let test;
function checkReturn() {
    if (!(test === undefined)) {
        return test;
    } else {
        return callMe('test');
    }
}
var data = checkReturn();
console.log(data); //output test
function callMe(val) {
    console.log(val);
}
// Shorthand
function checkReturn() {
    return test || callMe('test');
}

8. Short function calling
We can achieve these types of functions using ternary operator.

// Longhand
function test1() {
  console.log('test1');
};
function test2() {
  console.log('test2');
};
var test3 = 1;
if (test3 == 1) {
  test1();
} else {
  test2();
}
// Shorthand
(test3 === 1? test1:test2)();

9. Switch shorthand

We can save the conditions in the key-value objects and can be used based on the conditions.

// Longhand
switch (data) {
  case 1:
    test1();
  break;

  case 2:
    test2();
  break;

  case 3:
    test();
  break;
  // And so on...
}

// Shorthand
var data = {
  1: test1,
  2: test2,
  3: test
};

data[anything] && data[anything]();

10. Multi-line String Shorthand
When we are dealing with a multi-line string in code we can do it this way:

//longhand
const data = 'abc abc abc abc abc abc\n\t'
    + 'test test,test test test test\n\t'
//shorthand
const data = `abc abc abc abc abc abc
         test test,test test test test`

11.Implicit Return Shorthand

With the use of arrow functions, we can return the value directly without having to write a return statement.

Longhand:
//longhand
function getArea(diameter) {
  return Math.PI * diameter
}
//shorthand
getArea = diameter => (
  Math.PI * diameter;
)

12.Lookup Conditions Shorthand

If we have code to check the type and based on the type need to call different methods we either have the option to use multiple else ifs or go for the switch, but what if we have better shorthand than that?

// Longhand
if (type === 'test1') {
  test1();
}
else if (type === 'test2') {
  test2();
}
else if (type === 'test3') {
  test3();
}
else if (type === 'test4') {
  test4();
} else {
  throw new Error('Invalid value ' + type);
}
// Shorthand
var types = {
  test1: test1,
  test2: test2,
  test3: test3,
  test4: test4
};

var func = types[type];
(!func) && throw new Error('Invalid value ' + type); func();

13.Object.entries()

This feature helps to convert the object to an array of objects.

const data = { test1: 'abc', test2: 'cde', test3: 'efg' };
const arr = Object.entries(data);
console.log(arr);
/** Output:
[ [ 'test1', 'abc' ],
  [ 'test2', 'cde' ],
  [ 'test3', 'efg' ]
]
**/

14. Object.values()
This is also a new feature introduced in ES8 that performs a similar function to Object.entries(), but without the key part:

const data = { test1: 'abc', test2: 'cde' };
const arr = Object.values(data);
console.log(arr);
/** Output:
[ 'abc', 'cde']
**/

15. Repeat a string multiple times

To repeat the same characters again and again we can use the for loop and add them in the same loop but what if we have a shorthand for this?

//longhand 
let test = ''; 
for(let i = 0; i < 5; i ++) { 
  test += 'test '; 
} 
console.log(str); // test test test test test 
//shorthand 
'test '.repeat(5);

16. Power Shorthand

Shorthand for a Math exponent power function:

//longhand
Math.pow(2,3); // 8
//shorthand
2**3 // 8

17. Numeric Separators

You can now easily separate numbers with just an _ . This will make life of developers working with large numbers more easier.

//old syntax
let number = 98234567

//new syntax
let number = 98_234_567

If you would like to get update yourself with the latest features of JavaScript newest version(ES2021/ES12) check below:

1. replaceAll(): returns a new string with all matches of a pattern replaced by the new replacement word.

2.Promise.any(): It takes an iterable of Promise objects and as one promise fulfills, return a single promise with the value.

3. weakref: This object holds a weak reference to another object without preventing that object from getting garbage-collected.

4. FinalizationRegistry: Lets you request a callback when an object is garbage collected.

5. Private visibility: modifier for methods and accessors: Private methods can be declared with #.

6. Logical Operators: && and || operators.

7. Intl.ListFormat: This object enables language-sensitive list formatting.

8. Intl.DateTimeFormat: This object enables language-sensitive date and time formatting.

Conclusion
What's more, there we have it. 17 ways to optimize your code with modern JavaScript techniques.

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Stay safe 🏠

Top comments (52)

Elio Struyf • Jan 26 '21

Great list, just one thing in tip number 6 foreach Loop Shorthand. A for...in is not the same as a for...of loop!

With the for...in you iterate over the object its properties. For the for...in with an array, you'll get the index value.

With the for...of you iterate over all elements inside the array, so i will be the element and not the index.

Bruce Axtens • Feb 4 '21

Thanks for pointing that out, @estruyf . The following deno session demonstrates

> const b = "abcdef".split("")
undefined
> b
[ "a", "b", "c", "d", "e", "f" ]
> for (let x in b) console.log(x)
0
1
2
3
4
5
undefined
> for (let x of b) console.log(x)
a
b
c
d
e
f
undefined

DenisDiachenko • Jan 26 '21

That's a good list, just one thing I would like to mention in tips 4 and 5. It's better to check if the value is null or undefined using Nullish Coalescing Operator (??) since for some cases it might be an unexpected behavior:

const foo = null || 42;
console.log(foo);
// expected output: 42

const foo = 0 || 42;
console.log(foo);
// expected output: 0, but will be 42

So, in that case ?? will work as expected

const baz = 0 ?? 42;
console.log(baz);
// expected output: 0 and will be 0

Thank you for your work!

Blessing Hirwa • Jan 26 '21

In some cases Nullish Coalescing Operator is the best choice. Thanks for the assistance.

Andrew Bridge • Jan 25 '21

There are some good tips here! I hadn't come across the numeric separators, and it's great to see a replaceAll method after years of having to reach for a regex for that simple task!

One thing I'd note is being careful with falsey checks, in #3 your Longhand version would allow any value other than those you've specified. The Shorthand version would also fail the value 0 and false. If you're working with numbers, that can cause tricky to find bugs later on.

The other bit may be more of a preference but nested ternary statements or function calls via a ternary (as in #8) are quite hard to read compared to the "long" alternative and that could make it far more susceptible to bugs and harder to find it when it comes up. I'd far prefer 5 clear lines of code and let my minifier convert it to a one liner before I push my code live!

Anyway, great list! Thanks!

Juan A. Fuentest Torcat • Jan 30 '21

+1 I would advise to not nest two or more ternary operations. Also avoid it entirely if it means you'll get a single like 100+ characters long, or 120 depending on preference. But more than that usually means your code will be hard to read

Matthias Perktold • Jan 30 '21

When I have nested ternaries, I format them this way:

ˋˋˋjavascript
let test2 = (x > 100) ? 'greater 100'
: (x < 50) ? 'less 50'
: 'between 50 and 100';
ˋˋˋ

IMHO this reads quite nicely, since every condition is paired with the corresponding result, similar to a ˋswitchˋ block or an if-elseif-else chain.

Still, you shouldn‘t push it too far. When the conditions or value expressions get long, this becomes unreadable as well.

Andrew Bridge • Jan 30 '21 • Edited

I agree, it reads nicely enough, but what's the benefit to this over:

let test2 = 'between 50 and 100';
if (x > 100) { test2 = 'greater 100'; }
else if (x < 50) { test2 = 'less 50'; }

It's dealers choice with regard to using an else statement or default assignment as above and the formatting isn't my cup of tea, but it's still nevertheless the same statement on three lines. IMO, this is still way clearer and I don't see any downside to it.

Blessing Hirwa • Jan 30 '21

Long chained tenary operators are not good.

flyingCrp • Jan 26 '21

nice~
The code is used by the machine,and another function is to show it to people .
We have to make some trade-offs

Keven McDowell • Jan 26 '21

This list contains some good tips. Using an object in place of a switch statement is one of my favorite tricks to use. For your first tip, you may want to also consider using an object, since Array.includes is at worst a O(n) operation compared to an object lookup, which is a O(1) operation.

Sergey Ivanov • Jan 28 '21 • Edited

Code from the article, the second example:

// Longhand
let test: boolean;
if (x > 100) {
    test = true;
} else {
    test = false;
}
// Shorthand
let test = (x > 10) ? true : false;

It could be shorter, like the following:

let test = x > 10;

It could be not easy to read or understand several ternary operators in one and the same statement sometimes

Shorter not means better!

shadowtime2000 • Jan 26 '21

When I hear optimization I think making the file size smaller and having the code run faster, not refactors that make the code a lot cleaner.

z2lai • Jan 28 '21

True, this title definitely needs to be renamed to Clean Code tips as it's quite helpful.

zach • Jan 27 '21

These tips are really good.

Generally, I feel that using switch statements is most of the time not necessary, and using an object is very much a good alternative and one that is commonly available.

That being said, I think number 9 is misleading. You stated that objects are shorthand for switch statements, and they aren't. They're an alternative you could do sometimes. But saying an object is "shorthand" for a switch statement is definitely not correct.
There are definitely situations where you would need a switch statement instead of an object (IE, the object cannot replace the switch statement). A shorthand of syntax should be able to replace the original in all situations.

I think just modifying the text to state that its not a shorthand but an alternative that's commonly available would be good.

FADHILI Josue • Sep 17 '23 • Edited

this is for making clear the use of for...in and for...of

In JavaScript, for...in and for...of are both loop constructs used to iterate over data structures, but they are used for different purposes and work with different types of collections.

for...in:
The for...in loop is used to iterate over the properties of an object. It works with enumerable properties, which include both own properties and inherited properties from the object's prototype chain.

for (variable in object) { // code to be executed }
Usage:
`const person = {
name: 'fadhili',
age: 30,
city: ''rwanda
};

for (let key in person) {
console.log(key + ': ' + person[key]);
}
// that will loop in object keys(name, age, city)
//it will output object key: object value`

for...of:
The for...of loop is used to iterate over the elements of an iterable object. Iterable objects include arrays, strings, sets, maps, and other data structures that have a defined iteration protocol.

for (variable of iterable) { // code to be executed }
Usage:

`const colors = ['red', 'green', 'blue'];

for (let color of colors) {
console.log(color);
}
//In this example, for...of is used to loop through the elements ('red', 'green', 'blue') of the colors array.`

Key Differences:

1. Iterating Over:

for...in: Iterates over object properties.
for...of: Iterates over iterable values (e.g., elements in an array).

2. Iteration Variables:

for...in: Iterates over property names (keys).
for...of: Iterates over values.

3. Suitable for:

for...in: Best used for objects and when you need to enumerate object properties.
for...of: Best used for iterating over iterable collections like arrays and strings.

4. Works With:

for...in: Works with objects, including their inherited properties.
for...of: Works with iterables, including arrays, strings, sets, maps, etc.

5. Order of Iteration:

for...in: The order of iteration is not guaranteed and may vary between JavaScript engines.
for...of: Iterates in the order the elements appear in the collection.

6. Compatibility:

for...in: Supported in all modern browsers and older versions of JavaScript.
for...of: Introduced in ES6 and may not be supported in older browsers without

7. transpilation.
Remember to use for...in when you need to iterate over object properties and for...of when you're working with iterable collections like arrays or strings.

Jupiter Programmer • Jan 25 '21

real experience!!!

Ram Kumar Basak • Jan 29 '21

I am getting " Uncaught SyntaxError: expected expression, got keyword 'throw' " error while declaring this statement (!func) && throw new Error('Invalid value ' + type);