CODEWITHSUNDEEP
javascriptcomparisondeepequals
Yellowfun
Yellowfun

Reputation: 558

JS function "Deep comparison". Object comparison

I wanted to implement JS function "Deep comparison" and encounter on one interesting feature.

1st case - 

var arrValuesObjA = [{is: "an"}, 2];
var arrValuesObjB = [{is: "an"}, 2];

console.log(Array.isArray(arrValuesObjA), arrValuesObjA);
//true Array [ {…}, 2 ]   // 0: Object { is: "an" } 1: 2 length: 2
console.log(Array.isArray(arrValuesObjB), arrValuesObjB);
// true Array [ {…}, 2 ]  // 0: Object { is: "an" } 1: 2 length: 2


for (let i = 0; i < arrValuesObjA.length; i++) {
  console.log(arrValuesObjA[i] === arrValuesObjB[i]);
  // First iteration - false,   second iteration - true.
  // Means Object { is: "an" } from arrValuesObjA[0] don't equal to Object { is: "an" } from arrValuesObjB[0] !!!
}

But look into the 2nd case.

2nd case - 

let objA = {here: {is: "an"}, object: 2}, objB = {here: {is: "an"}, object: 2};

var arrKeysObjA = Object.keys(objA);
var arrKeysObjB = Object.keys(objB);
var arrValuesObjA = [];
var arrValuesObjB = [];

for (let i = 0; i < arrKeysObjA.length; i++) {
  arrValuesObjA.push(objA[arrKeysObjA[i]]);
}

for (let i = 0; i < arrKeysObjB.length; i++) {
  arrValuesObjB.push(objA[arrKeysObjB[i]]);
}

console.log(Array.isArray(arrValuesObjA), arrValuesObjA);
// true Array [ {…}, 2 ]   // 0: Object { is: "an" } 1: 2 length: 2 // the same as in 1st case!
console.log(Array.isArray(arrValuesObjB), arrValuesObjB);
// true Array [ {…}, 2 ]   // 0: Object { is: "an" } 1: 2 length: 2 // the same as in 1st case!

for (let i = 0; i < arrKeysObjA.length; i++) {
  console.log(arrValuesObjA[i] === arrValuesObjB[i]);
  // First iteration - true!!!,   second iteration - true.
  // Means Object { is: "an" } from arrValuesObjA[0] equal to Object { is: "an" } from arrValuesObjB[0] !!!
}

In 1st case Object { is: "an" } from arrValuesObjA[0] don't equal to Object { is: "an" } from arrValuesObjB[0] but in the 2nd case they are equal.

Can anyone explain what's going on? I think it somehow related with copy by value and copy by reference but i'm not sure.

Upvotes: 1

Views: 151

Answers (1)

Giorgi Moniava
Giorgi Moniava

Reputation: 28654

for (let i = 0; i < arrKeysObjA.length; i++) {
    arrValuesObjA.push(objA[arrKeysObjA[i]]);
}

for (let i = 0; i < arrKeysObjB.length; i++) {
    arrValuesObjB.push(objA[arrKeysObjB[i]]);
}

Look carefully in both cases above you are using objA.

Upvotes: 1

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