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javascript interview questions

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List of Javascript fun Questions

Some are very basic programming questions that are designed to show how a person thinks.


Remove overlapping matches in Array

Givven an array of numbers, and a size parameter, the getNotOverlapping is expected to return a new array with equal or less item, which their values do not overlap in accordance to the size variable.

function getNotOverlapping(arr, size){  
}

console.log(
  getNotOverlapping([0,1,2,3], 1), // 0,1,2,3
  getNotOverlapping([0,1,2,3], 2)  // 0,2
)
See Answer 
[1, 2, 3, 4].reduce((acc, item, idx) =>  
idx === 0 || acc[acc.length-1] + size <= item ?
    [...acc, item]
    : acc, [])

Create an array of N length and fill each item by it's index number

https://itnext.io/heres-why-mapping-a-constructed-array-doesn-t-work-in-javascript-f1195138615a

See Answer 
[...new Array(5)].map((_, idx) => idx)

Remove empty elements from Array

[1,2,null,undefined,3,,"3",,NaN,0,,,true,false, {}]
See Answer 
.filter(Boolean)

Make Array.indexOf() case insensitive

See Answer 
["Foo", "foO", "foo"].findIndex(item => item.toLowerCase() == 'foo')

Find second largest number in an unsorted Array of numbers

See Answer

https://stackoverflow.com/a/17040125/104380

Limit a number to be between 0 & 100

See Answer 
Math.max(0, Math.min(100, num))

Get the avarage of a number's digits

See Answer

https://stackoverflow.com/a/18234568/104380

'1234'.split('').reduce((result, digit, idx, arr) => 
    (result + +digit)/(idx == arr.length-1 ? arr.length : 1)
, 0)

Or:

let num = '12345';
let sum = 0

for( let d of num )
  sum += +d

console.log(sum/num.length) // 3

Check if an array contains only numbers

See Answer 
![1,2,"3"].some(item => typeof item !== "number")

Flip an integer (123 -> 321). suggest more than one solution.

https://stackoverflow.com/a/52366332/104380

Sum two binary numbers (using as low-level code as possible)

1011 + 11 // => 1110

https://stackoverflow.com/a/52372514/104380

Split a paragraph into segments of max N characters, without word-breaking

Check if a variable is an Object {}

Create a function which executes once

State different ways to define a function and their differences

How to convert a DOM node list (HTMLCollection) into an array?

Add only unique objects to an array

Determine if two Objects are equal (identical to previous question, but more explicit)

Remove DOM event listener which was added with callback which used ".bind()"

function Example(name){
	this.name = name;
	window.addEventListener("click", this.clicked.bind(this))
}

Example.prototype.clicked = function(){
	console.log(this.name)
}

Example.prototype.destroy = function(){
	...
}

const example = new Example('foo')

Flatten multidimensional (2D) Array

var arr = [[1,2],[3,4],[5,6]]
console.log( [].concat(...arr) )

// ES2015 "flat":
arr.flat();

Check how many times each digit in a number repeats itself

1201977 => [[1,2], [2,1], [0,1], [9,1], [7,2]]

Check number for duplicate digits

[1, 10, 11, 1010, 1981] => [false, false, true, true, true]

What would be the output of this?

[1,2] + [3,4]

Repeat a String N times

Arguments vs Parameters, which term means what

Check if character is number

https://stackoverflow.com/questions/8935632/check-if-character-is-number/32572539#32572539

Enhance console.log function to print your name before, and as part of, the rest of the log

What would these print:

var foo = (...a) => console.log(a);
foo([1,2,3], 4)

var foo = (...[a]) => console.log(a);
foo([1,2,3], 4)

For N arrays of varrying length in a 2D array, get the longest array's index

https://stackoverflow.com/a/57491707/104380

Write a function which finds a DOM node's index within its parent node

Deep-clone the Array & remove the 2nd item

See Answer 
[{a:1}, {b:2}, {c:3}].reduce((newArr, item, idx) => {
    if( idx != 1 )
        newArr.push({...item})
    return newArr
}, [])

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javascript interview questions