Clone a js object except for one key

Question

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)?

Answer 1

If you're dealing with a huge variable, you don't want to copy it and then delete it, as this would be inefficient.

A simple for-loop with a hasOwnProperty check should work, and it is much more adaptable to future needs :

for(var key in someObject) {
        if(someObject.hasOwnProperty(key) && key != 'undesiredkey') {
                copyOfObject[key] = someObject[key];
        }
}

Answer 2

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"]);

Answer 3

You also can use spread operator to do this

const source = { a: 1, b: 2, c: 3, z: 26 }
const copy = { ...source, ...{ b: undefined } } // { a: 1, c: 3, z: 26 }

Answer 4

Maybe something like this:

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

Is this good enough? Or can't c actually get copied?

Answer 5

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

_.omit(x, 'b')

Or ramda.

R.omit('b', x)

Answer 6

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