Frequently Asked Javascript Interview Questions

bind.js

Function.prototype.bind1 = function (scope) {
  let fn = this
  let prefixArgs = Array.prototype.slice.call(arguments, 1)
  
  return function() {
    let suffixArgs = Array.prototype.slice.call(arguments)
    let args = prefixArgs.concat(suffixArgs)
    return fn.apply(scope, args)
  } 
}

// Ex 1: Create a function with a preset leading argument
function list() {
  // arguments is an array-like object. convert arguments to an array.  
  return Array.prototype.slice.call(arguments);
}
console.log( list(1, 2, 3) ) // [1, 2, 3]

var leadingThirtysevenList = list.bind1(null, 37)
console.log( leadingThirtysevenList() ) // [37]
console.log( leadingThirtysevenList(1, 2, 3) ) // [37, 1, 2, 3]

// Ex 2: Changing the scope of `this`
var foo = {
  x: 3
}

function bar (){
  console.log(this.x)
}

var boundFunc = bar.bind1(foo)
boundFunc() // 3

curry1.js

let sentence = ''

function say () {

  if ( !arguments[0] ) {
    let s = sentence
    sentence = ''
    return s
  } else {      
    sentence += arguments[0] + ' '
    // Note: This is not a recursion
    return say
  }

}

console.log( say('Foo')('bar')() ) // => "Foo bar "
console.log( say('Hi')('my')('name')('is')('Foo')() ) // "Hi my name is Foo "

curry2.js

function add10 (a) {
  return a + 10
}

function compound (f) {
  return function (b) {
    return f(f(b))
  }
}

console.log( add10(10) ) // 20
console.log( compound(add10)(10) ) // 30

customSetInterval.js

function customSetInterval (cb, interval) {
  return setTimeout( () => {
    if (typeof cb == 'function') {
      cb()
      // Recurse
      customSetInterval(cb, interval)
    } else {
      console.error(new Error('Expecting a function as a callback'))
    }
  }, interval)
}

function resetCustomSetInterval (id) {
  clearTimeout(id)
}

function hello (){
  console.log('hello')
}
 
let id = customSetInterval(hello, 1000)

let id2 = customSetInterval('hello', 1000) // [Error: Expecting a function as a callback]

hexToRGB.js

function hexToRGB (hex) {
  
  // remove whitespace from left and rihgt ends
  hex = hex.trim()
  if (hex.startsWith('#')) {
    hex = hex.replace('#', '')
  }
  
  // convert short hand notation (f0f) to the regular notation (ff00ff)
  if (hex.length == 3) {
    let temp = ''
    for (let i = 0; i < hex.length; i++)
      temp += hex[i] + hex[i]
    hex = temp
  }

  // check for additional white space between characters (f    0    f)
  if (hex.length != 6 ) {
    throw new Error(`hexToRGB was called with incorrect hex code. 
      Valid hex code is either three to four characters long with following characters '0123456789ABCDEFabcdef' `)
  }

  // check for valid characters from 0-F
  let validHexChars = '0123456789ABCDEFabcdef' 
  for (let i = 0; i < hex.length; i++) {
      if ( !validHexChars.includes(hex[i]) ) {
        throw new Error(`hexToRGB was called with incorrect hex code. 
          Valid hex code is either three to four characters long with following characters '0123456789ABCDEFabcdef' `)        
      }
  }
  
  let RGB = []
  let r = parseInt(hex.substring(0, 2), 16)
  RGB.push(r)
  let g = parseInt(hex.substring(2, 4), 16)
  RGB.push(g)
  let b = parseInt(hex.substring(4, 6), 16)
  RGB.push(b)

  return RGB
}

//console.log( hexToRGB('ff00ff') ) // [255, 0, 255]
//console.log( hexToRGB('#ff00ff') ) // [255, 0, 255]
//console.log( hexToRGB('#f0f') ) // [255, 0, 255]
//console.log( hexToRGB('ff00fff') ) // hextToRGB was called with incorrect hex code. ...
//console.log( hexToRGB('ff00ffg') ) // hextToRGB was called with incorrect hex code. ...

ticTacToeWinner.js

const BOARD_SIZE = 3
// For 3 * 3 board, stateOfTheGame  = [row1, row2, row3, col1, col2, col3, diag1, diag2]
let stateOfTheGame = new Array(BOARD_SIZE * 2 + 2)
//Initialize the board with zero
stateOfTheGame.fill(0)

function isTicTacToeWon (row, column, player) {

  // We will use -1 for 'ZERO' and +1 for player 'EX'
  let point = (player == 'ZERO') ? -1 : 1

  // At every step we will have to update the relevant row, column and diagonal

  // update row
  stateOfTheGame[row] += point
  // update column
  stateOfTheGame[BOARD_SIZE + column] += point
  // update diagonal1
  if (row == column) {
    stateOfTheGame[2*BOARD_SIZE] += point
    // case (2, 2) in 3 * 3 Board
    let shouldUpdateDia2 = (BOARD_SIZE + 1) / 2 == column ? true : false;
    if (shouldUpdateDia2) {
    	stateOfTheGame[2*BOARD_SIZE + 1] += point
    }
  }
  // update diagonal2
  if (row + column == BOARD_SIZE + 1) {
    stateOfTheGame[2*BOARD_SIZE + 1] += point
  }

  // We finish updating the game board. Let's see if we have a winner or not
  let i = stateOfTheGame.indexOf(3)
  let j = stateOfTheGame.indexOf(-3)

  // If we have 3, -3 in the array it means we have a winner
  return (i >= 0 || j >= 0) ? true : false;
}

console.log( isTicTacToeWon(0, 0, 'ZERO') ) // false
console.log( isTicTacToeWon(0, 1, 'ZERO') ) // false
console.log( isTicTacToeWon(0, 2, 'ZERO') ) // true

The resetCustomSetInterval function not work in customSetInterval.js line 14 if it has run once. because each setTimeout return a new handle id