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JavaScript Quiz Part 2

Sai gowtham on July 07, 2018

If you want to answer part1 check out part1 1.How to reverse a String Using Reduce Method. example: if you pass 'king' as an argument output is...

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Avalander • Jul 7 '18 • Edited

1.How to reverse a String Using Reduce Method.

const reverseStr = str =>
    (str.split('')
        .reduce((prev, c) => ([ c, ...prev ]), [])
        .join(''))

3.How to convert an object into a string?

Kinda depends on what you want.

const pony = {
    name: 'Twilight Sparkle',
    type: 'Unicorn',
    element: 'Magic',
}

// Option A because nothing beats '[object Object]' as a string representation
pony.toString() // '[object Object]'

// Option B
JSON.stringify(pony) // '{"name": "Twilight Sparkle", "type": "Unicorn", "element": "Magic"}'

// Option C
pony.toString = function () {
    return `${this.name}, ${this.type}, ${this.element}`
}
pony.toString() // 'Twilight Sparkle, Unicorn, Magic'

// Option D
pony.inspect = function () {
    return `Pony(${this.name}, ${this.type}, ${this.element})`
}
pony.inspect() // 'Pony(Twilight Sparkle, Unicorn, Magic)'

// Option E because why not
pony.toString = function () {
    return `${this.name}, ${this.type}, ${this.element}`
}
pony + '' // 'Twilight Sparkle, Unicorn, Magic'

Florian Reuschel • Jul 9 '18

Interesting fact for completeness: The JSON counterpart of toString() is toJSON(). If an object has a toJSON() method, it will be evaluated and its result will be stringified instead:

pony.toJSON = function () {
  return this.name
}

JSON.stringify(pony) === '"Twighlight Sparkle"'

Avalander • Jul 9 '18

Nice! I wasn't aware of that!

Then we could potentially override that method to get [object Object] when converting it to JSON.

pony.toJSON = function () {
    return this.toString()
}

JSON.stringify(pony) // '[object Object]'

Florian Reuschel • Jul 9 '18

That sounds... useful? 🙈
But yeah, it's a feature that I as well only discovered after many years of JS experience and since have never used in production. It's pretty cool though.

Florian Reuschel • Jul 9 '18

Oh, and also the result would in fact be "[object Object]". The quotes are part of the serialized result (since it needs to be valid JSON).

Avalander • Jul 9 '18

That sounds... useful? 🙈

I mean, the specification is that the object gets converted to a string. About the actual content of the string, the OP said nothing 😝

ItsASine (Kayla) • Jul 7 '18

Slight error in your example: Twilight is an Alicorn. Source ❤️

Avalander • Jul 7 '18

Haha, good catch! I'd update my post but I'm too lazy, so let's say I'm referencing the first season.

Meghan (she/her) • Jul 7 '18 • Edited

// #1
"hello".split("").reduce((c,v,i,a) => c + a[a.length-i-1], "");

#2
// .slice returns a shallow copy of "substring" of elements in an Array
// .splice removes elements from elements at an index and can insert as well

#3
This is a bit of a trick question and depends on what you're looking for, and @avalander went into a lot of detail for this

Navneet Sahota • Jul 8 '18

1.How to reverse a String Using Reduce Method.

function reverseString(str) {
  const arr = str.split('');
  return arr.reduce((acc, val) => val + acc,"");
}

2.What is the difference between slice and splice?

Slice method is used to get some portion of the existing array/string.
Splice method actually mutates the existing array and can add or remove items from the array.

3.How to convert an object into a string?

Not Sure what you want as output. Others have explained it well though.

Lea Rosema (she/her) • Jul 11 '18 • Edited

"Hello World".split('').reduce((a, b) => b + a)
slice is a prototype function on Array and String. It doesn't mutate and returns a new Array/String that equals to an extract of the Array/String. splice is a prototype function on Array and is used to insert and delete elements at a given index of the array. It mutates the actual array and returns the deleted elements.
You can explicitly call obj.toString() or you can use JavaScript's coercion: (obj + ""), so the obj.toString() method is implicitly called to convert it to a string. By default, the output is not too useful; it returns [object Object], but you can override the toString() method. Or, if you want to serialize the object into a string representation, you may want to use JSON.stringify(obj)

Sai gowtham • Jul 11 '18

Wow i was expecting this answer for reversing a string you can even do

const stringRev = (str)=>[...str].reduce((acc,e)=>e+acc)

Florian Reuschel • Jul 9 '18 • Edited

1) How to reverse a string using reduce method?

const rev = str => [...str].reduce((carry, char) => char.concat(carry), '')

Specifically, [...str] is superior to str.split('') because it correctly handles Unicode:

'😎'.split('') // ["�", "�"]
[...'😎'] // ["😎"]

2) What is the difference between slice and splice?

slice copies a range out of an array. splice deletes and/or inserts items at a given position in an array.

3) How to convert an object into a string?

The question's a little to broad imo, I'm gonna spare the time writing out exactly what Avalander did.

jtkohne • Jul 9 '18

First I just want to say why would you ever need to use the reduce method when working with a string when you can just simply do some casting from a string to array the back, especially since all you're trying to do is reverse the string. Since a lot of have already answered the question for the reduce method I offer you these two solutions instead...

"king".split("").reverse().join(""); // result will be "gnik"

You could also accomplish this with a simple loop

var str = "king";
var reversed = "";
var i = str.length-1;
while (i >=0) {
reversed += str[i];
i--;
}
// result in the reversed variable will be "gink"

This one is constantly confused across JS developers. Splice actually returns a mutated version of the original array, and in the process actually modifies the array. Slice on the other hand can return a copy or a mutated version of the array, but the original array remains the way it was before the operation was executed. For example, if you try arr.splice(1, 1); it will literally remove a single item from an array starting at index 1. If you were to do the same thing with a slice operation, arr.slice(1, 1) it will start at index 1 and return 1 item in a new array (new array in memory). Splice also is used to manipulate arrays without the need to strore a returned result in a new variable since the original reference in memory is modified, whereas slice is intended to be used as a executable operation on an existing array and a returned value will either get passed as a parameter or stored in memory with it's own pointer and variable name.
Avalander's answer is pretty concise, but if I were to give an answer based on how the question is worded it would have to be JSON.stringify(obj);

YCM Jason • Jul 9 '18

reverseStr = ss => [ss].reduce(([...ss]) => ss.reverse().join(''));

Ben Halpern • Jul 8 '18

Loving these threads, Sai!

Sudeep Pandey • Jul 20 '18

var input = "king";
var reverseString = input.split("").reduce((accumulator, currentValue, index, array)=> currentValue + accumulator);

ItsASine (Kayla) • Jul 7 '18

ELI5 version of #2: Slice returns a new array while splice modifies the original reference

Sudeep Pandey • Jul 20 '18

slice doesn't modify the array and create a new array but splice modified the array