Native deep cloning
It's called "structured cloning", works experimentally in Node 11 and later, and hopefully will land in browsers. See this answer for more details.
Fast cloning with data loss - JSON.parse/stringify
If you do not use Date
s, functions, undefined
, Infinity
, RegExps, Maps, Sets, Blobs, FileLists, ImageDatas, sparse Arrays, Typed Arrays or other complex types within your object, a very simple one liner to deep clone an object is:
JSON.parse(JSON.stringify(object))
const a = {
string: 'string',
number: 123,
bool: false,
nul: null,
date: new Date(), // stringified
undef: undefined, // lost
inf: Infinity, // forced to 'null'
re: /.*/, // lost
}
console.log(a);
console.log(typeof a.date); // Date object
const clone = JSON.parse(JSON.stringify(a));
console.log(clone);
console.log(typeof clone.date); // result of .toISOString()
See Corban's answer for benchmarks.
Reliable cloning using a library
Since cloning objects is not trivial (complex types, circular references, function etc.), most major libraries provide function to clone objects. Don't reinvent the wheel - if you're already using a library, check if it has an object cloning function. For example,
- lodash -
cloneDeep
; can be imported separately via the lodash.clonedeep module and is probably your best choice if you're not already using a library that provides a deep cloning function
- AngularJS -
angular.copy
- jQuery -
jQuery.extend(true, { }, oldObject)
; .clone()
only clones DOM elements
- just library -
just-clone
; Part of a library of zero-dependency npm modules that do just do one thing.
Guilt-free utilities for every occasion.
ES6 (shallow copy)
For completeness, note that ES6 offers two shallow copy mechanisms: Object.assign()
and the spread syntax.
which copies values of all enumerable own properties from one object to another. For example:
var A1 = {a: "2"};
var A2 = Object.assign({}, A1);
var A3 = {...A1}; // Spread Syntax
JavaScript has a number formatter (part of the Internationalization API).
// Create our number formatter.
var formatter = new Intl.NumberFormat('en-US', {
style: 'currency',
currency: 'USD',
// These options are needed to round to whole numbers if that's what you want.
//minimumFractionDigits: 0, // (this suffices for whole numbers, but will print 2500.10 as $2,500.1)
//maximumFractionDigits: 0, // (causes 2500.99 to be printed as $2,501)
});
formatter.format(2500); /* $2,500.00 */
Use undefined
in place of the first argument ('en-US'
in the example) to use the system locale (the user locale in case the code is running in a browser). Further explanation of the locale code.
Here's a list of the currency codes.
Intl.NumberFormat vs Number.prototype.toLocaleString
A final note comparing this to the older .toLocaleString
. They both offer essentially the same functionality. However, toLocaleString in its older incarnations (pre-Intl) does not actually support locales: it uses the system locale. So when debugging old browsers, be sure that you're using the correct version (MDN suggests to check for the existence of Intl
). There isn't any need to worry about this at all if you don't care about old browsers or just use the shim.
Also, the performance of both is the same for a single item, but if you have a lot of numbers to format, using Intl.NumberFormat
is ~70 times faster. Therefore, it's usually best to use Intl.NumberFormat
and instantiate only once per page load. Anyway, here's the equivalent usage of toLocaleString
:
(2500).toLocaleString('en-US', {
style: 'currency',
currency: 'USD',
}); /* $2,500.00 */
Some notes on browser support and Node.js
- Browser support is no longer an issue nowadays with 98% support globally, 99% in the US and 99+% in the EU
- There is a shim to support it on fossilized browsers (like Internet Explorer 8), should you really need to
- Node.js before v13 only supports
en-US
out of the box. One solution is to install full-icu, see here for more information
- Have a look at CanIUse for more information
Best Answer
Easy.