Javascript : Guess output of the code

Guess output of the code.

Code:

//first question

var obj = {

    a: 1,

    b: 2,

    add: function () {

        return this.a + this.b;

    }

}

var r = obj.add();

console.log("r=" + r);

//second question

var obj1 = {

    a: 1,

    b: 2,

    add: function () {

        return this.a + this.b;

    }

}

var s = obj1.add;

console.log("s=" + s());

//third question

var s1 = obj1.add;

s2 = s1.bind(obj1);

console.log("s2=" + s2());

Output:

        r=3

        s=NaN

s2=3

Notes:

wrt obj1.add here s contains the function, but the connection

to obj1 is not retained.In non-strict mode, JavaScript sets: this = globalThis

deep copy nested object

  Write a code to deep copy nested object.

Code:

var obj ={

    name:"sangram",

    address:{

        city:"mumbai",

        state:"maharashtra",

        pin:"4000**",

office:null,

        contactNo:{

            "landline":"***67-554569",

            "mobile":"**78456729",

        }

    }

}

function deepCopy(obj){

    var deepCopied={}

    for(let key in obj){

        if (obj[key] !== null || typeof obj[key] !== "object") {

            deepCopied[key] = obj[key]

        }else{

            deepCopied[key] = deepCopy(obj[key])

        }

    }

    return deepCopied

}

let x = deepCopy(obj);

console.log("Final Output:",x)

Output:

Final Output: {

  name: 'sangram',

  address: {

    city: 'mumbai',

    state: 'maharashtra',

    pin: '4000**',

office:null,

    contactNo: { landline: '***67-554569', mobile: '**78456729' }

  }

}

Note:deepcopy & deepclone term are used interchangeably in interviews & discussion.

Compare boolean with empty array

Guess output of following program

console.log(Boolean([]));   // true

console.log(![]);           // false

console.log(false == []);   // true

console.log(false == ![]);  // true

Output:

        true

        false

        true

        true

Explation in 3rd line

        console.log(false == []); // false == "" then 0 == 0 then true

In 4t line

        console.log(false == ![]);  //  false == ! true then false == false then true

Type Coercion in comparison

in == type coersion happens in === does not.In == for string comparison

toString method on object is called which can be overridden to get desired

result.

Code :

        const pre={}

       

        console.log(pre.toString()); // "[object Object]"

        const obj = {

        toString() {

        return "{}";

        }

        }

        console.log(obj.toString()); // "{}"

        console.log(obj == "{}");    // true

        console.log(obj === "{}");   // false

Output:

        [object Object]

        {}

        true

false 

Group By Object array based on provided key

Group by following object array based on key "city".

const users = [

  {

    name: "sangram",

    city: "kankavali"

  },

  {

    name: "sagar",

    city: "malvan"

  },

  {

    name: "sachin",

    city: "kankavali"

  }

];

Code :

const users = [

  {

    name: "sangram",

    city: "kankavali"

  },

  {

    name: "sagar",

    city: "malvan"

  },

  {

    name: "sachin",

    city: "kankavali"

  }

];

let obj = {};

let output = users.reduce((acc, item) => {

  if (!acc[item.city]) {

    acc[item.city] = [];

  }

  acc[item.city].push(item);

  return acc;

}, obj);

console.log("Final Output:", output);

Output:

Final Output: {

  kankavali: [

    { name: 'sangram', city: 'kankavali' },

    { name: 'sachin', city: 'kankavali' }

  ],

  malvan: [ { name: 'sagar', city: 'malvan' } ]

}

Second Largest Number in Array

 Given an array find second largest number

Code

let arr=[12,9,13,34,-45,12,67]

let unique = [...new Set(arr)]

console.log("Unique Array:",unique)

unique.sort((a,b)=>b-a)

console.log("Sorted Array:",unique)

console.log("Second Largest Number:",unique[1])

Output:

        [ 12, 9, 13, 34, -45, 67 ]

        [ 67, 34, 13, 12, 9, -45 ]

        Second Largest Number: 34

In form of function:

function findNthLargest(arr,n){

    let unique = [...new Set(arr)]

    unique.sort((a,b)=>b-a)

    if (unique.length < n){

        throw new Error("Array can't have nth largest number")

    }else{

        return unique[n-1]

    }

}

let arr=[12,9,13,34,-45,12,67]

let n=3

console.log(n + "th Largest Number:" + findNthLargest(arr,n))

Output:

    3th Largest Number:13

       

In an Array move zero element to bottom of array

Given an array modify array in such a way that all

zero element are at end non zero element at front

Code

var arr=[5,8,-45,0,6,0,10,-1,67];

console.log("Original Array",arr)

let nonZero = arr.filter((item)=>{

 return item !=0

})

let zero = arr.filter((item)=>{

 return item ==0

})

arr = [...nonZero,...zero]

console.log("Final Output:",arr)

Output:

    Original Array [

    5,  8, -45,  0, 6,

    0, 10,  -1, 67

    ]

    Final Output: [

    5,  8, -45, 6, 10,

    -1, 67,   0, 0

    ]

Another way

var arr = [5, 8, -45, 0, 6, 0, 10, -1, 67];

let j = 0;

for (let i = 0; i < arr.length; i++) {

    if (arr[i] !== 0) {

        [arr[i], arr[j]] = [arr[j], arr[i]];

        j++;

    }

}

console.log("Final Output:", arr)