CODEWITHSUNDEEP
javascriptecmascript-6
Fellow Stranger
Fellow Stranger

Reputation: 34023

Comparing a subset of properties between objects

I have a pretty naive way to compare a subset of two objects’ properties with each other. It gets hard to read when there are many properties in the subset. What could be some alternatives?

const obj1 = {a: 22, b: 33, c: 44};
const obj2 = {a: 22, b: 34, c: 44};

JSON.stringify([obj1.a, obj1.b]) === JSON.stringify([obj2.a, obj2.b])

Upvotes: 1

Views: 973

Answers (3)

Mike Ezzati
Mike Ezzati

Reputation: 3166

Subset comparison : SubsetCompare function does a flat comparison of a subset of two objects.

let obj1 = {a: 22, b: 34, c: 44};
let obj2 = {a: 22, b: 34, c: 10};

let subsetCompare = (obj1, obj2, keys) =>  keys.every(key =>  obj1[key] === obj2[key]);

console.log(subsetCompare(obj1, obj2, ['a', 'b']));

console.log(subsetCompare(obj1, obj2, ['a', 'b', 'c']))

Flat comparison : flatCompare function only compares value of primitive type members and reference of reference type members.

let x = { a : 10};
let y = { a : 10};
let obj1 = {a: 22, b: 34, c: 44, d:y};
let obj2 = {a: 22, b: 34, c: 44, d:x};

let flatCompare = (obj1, obj2) => {
  let keys = [];
  if((keys = getKeys(obj1)).length != getKeys(obj2).length)
    return false;
  return keys.every(key => obj1[key] === obj2[key]);
}

let isObject = (obj) => obj === Object(obj);

let getKeys = (obj) => Object.getOwnPropertyNames(obj);

console.log(flatCompare(obj1, obj2));

Deep comparison : deepCompare function recursively compares also values of primitive type members of nested objects.

let x = { a : 10};
let y = { a : 10};
let obj1 = {a: 22, b: 34, c: 44, d:y};
let obj2 = {a: 22, b: 34, c: 44, d:x};


let deepCompare = (obj1, obj2) => {
  let keys = [];
  if((keys = getKeys(obj1)).length != getKeys(obj2).length)
    return false;
  return keys.every(key => {
    if(isObject(obj1[key]) && isObject(obj2[key]))
      return deepCompare(obj1[key], obj2[key]);
    return obj1[key] === obj2[key];
  });
};

let isObject = (obj) => obj === Object(obj);

let getKeys = (obj) => Object.getOwnPropertyNames(obj);

console.log(deepCompare(obj1, obj2))

Upvotes: 3

Fellow Stranger
Fellow Stranger

Reputation: 34023

Based on @revilheart's answer but with @Ryan's every suggestion:

let obj1 = {a: 22, b: 33, c: 44};
let obj2 = {a: 22, b: 34, c: 44};
console.log(compareObjects(obj1, obj2, [`a`, `b`])); // false
console.log(compareObjects(obj1, obj2, [`a`, `c`])); // true
console.log(compareObjects(obj1, obj2, [`b`, `c`])); // false

function compareObjects(obj1, obj2, keys) {
  return keys.every(key => obj1[key] === obj2[key])
}

Upvotes: 0

rafaelgomesxyz
rafaelgomesxyz

Reputation: 1405

Why not use a function?

let obj1 = {a: 22, b: 33, c: 44};
let obj2 = {a: 22, b: 34, c: 44};
console.log(compareObjects(obj1, obj2, [`a`, `b`])); // false
console.log(compareObjects(obj1, obj2, [`a`, `c`])); // true
console.log(compareObjects(obj1, obj2, [`b`, `c`])); // false

function compareObjects(obj1, obj2, keys) {
    let i;
    for (i = keys.length - 1; i > -1 && obj1[keys[i]] === obj2[keys[i]]; i--);
    return i === -1; // if i equals -1 it went through the whole loop and did not fail for the second condition
}

Upvotes: 1

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