Clone a js object except for one key

Clone a js object except for one key

I have a flat JS object:
{a: 1, b: 2, c: 3, …, z:26}

I want to clone the object except for one element:
{a: 1, c: 3, …, z:26}

What’s the easiest way to do this (preferring to use es6/7 if possible)?

Solutions/Answers:

Solution 1:

If you use Babel you can use the following syntax to copy property b from x into variable b and then copy rest of properties into variable y:

let x = {a: 1, b: 2, c: 3, z:26};
let {b, ...y} = x;

and it will be transpiled into:

"use strict";

function _objectWithoutProperties(obj, keys) { var target = {}; for (var i in obj) { if (keys.indexOf(i) >= 0) continue; if (!Object.prototype.hasOwnProperty.call(obj, i)) continue; target[i] = obj[i]; } return target; }

var x = { a: 1, b: 2, c: 3, z: 26 };
var b = x.b;

var y = _objectWithoutProperties(x, ["b"]);

Solution 2:

var clone = Object.assign({}, {a: 1, b: 2, c: 3});
delete clone.b;

or if you accept property to be undefined:

var clone = Object.assign({}, {a: 1, b: 2, c: 3}, {b: undefined});

Solution 3:

To add to Ilya Palkin’s answer: you can even dynamically remove keys:

const x = {a: 1, b: 2, c: 3, z:26};

const objectWithoutKey = (object, key) => {
  const {[key]: deletedKey, ...otherKeys} = object;
  return otherKeys;
}

console.log(objectWithoutKey(x, 'b')); // {a: 1, c: 3, z:26}
console.log(x); // {a: 1, b: 2, c: 3, z:26};

Demo in Babel REPL

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Source:

Solution 4:

For those who can’t use ES6, you can use lodash or underscore.

_.omit(x, 'b')

Or ramda.

R.omit('b', x)

Solution 5:

You can write a simple helper function for it. Lodash has a similar function with the same name: omit

function omit(obj, omitKey) {
  return Object.keys(obj).reduce((result, key) => {
    if(key !== omitKey) {
       result[key] = obj[key];
    }
    return result;
  }, {});
}

omit({a: 1, b: 2, c: 3}, 'c')  // {a: 1, b: 2}

Also, note that it is faster than Object.assign and delete then: http://jsperf.com/omit-key

Solution 6:

I use this one-liner ES6 syntax,

const obj = {a: 1, b: 2, c: 3, d: 4};
const clone = (({b, c, ...others}) => ({...others}))(obj); // remove b and c
console.log(clone);