How can I clone a JavaScript object except for one key?

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});

I use this ESNext one liner

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

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"]);