How can I merge properties of two JavaScript objects dynamically?
I need to be able to merge two (very simple) JavaScript objects at runtime. For example I'd like to:
var obj1 = { food: 'pizza', car: 'ford' }
var obj2 = { animal: 'dog' }
obj1.merge(obj2);
//obj1 now has three properties: food, car, and animal
Does anyone have a script for this or know of a built in way to do this? I do not need recursion, and I do not need to merge functions, just methods on flat objects.
ECMAScript 2018 Standard Method
You would use object rest spread:
let merged = {...obj1, ...obj2};
/** There's no limit to the number of objects you can merge.
* Later properties overwrite earlier properties with the same name. */
const allRules = {...obj1, ...obj2, ...obj3};
ECMAScript 2015 (ES6) Standard Method
/* For the case in question, you would do: */
Object.assign(obj1, obj2);
/** There's no limit to the number of objects you can merge.
* All objects get merged into the first object.
* Only the object in the first argument is mutated and returned.
* Later properties overwrite earlier properties with the same name. */
const allRules = Object.assign({}, obj1, obj2, obj3, etc);
(see MDN JavaScript Reference)
Method for ES5 and Earlier
for (var attrname in obj2) { obj1[attrname] = obj2[attrname]; }
Note that this will simply add all attributes of obj2 to obj1 which might not be what you want if you still want to use the unmodified obj1 .
If you're using a framework that craps all over your prototypes then you have to get fancier with checks like hasOwnProperty , but that code will work for 99% of cases.
Example function:
/**
* Overwrites obj1's values with obj2's and adds obj2's if non existent in obj1
* @param obj1
* @param obj2
* @returns obj3 a new object based on obj1 and obj2
*/
function merge_options(obj1,obj2){
var obj3 = {};
for (var attrname in obj1) { obj3[attrname] = obj1[attrname]; }
for (var attrname in obj2) { obj3[attrname] = obj2[attrname]; }
return obj3;
}
jQuery also has a utility for this: http://api.jquery.com/jQuery.extend/.
Taken from the jQuery documentation:
// Merge options object into settings object
var settings = { validate: false, limit: 5, name: "foo" };
var options = { validate: true, name: "bar" };
jQuery.extend(settings, options);
// Now the content of settings object is the following:
// { validate: true, limit: 5, name: "bar" }
The above code will mutate the object named settings .
If you want to create a new object without modifying either argument, use this:
var defaults = { validate: false, limit: 5, name: "foo" };
var options = { validate: true, name: "bar" };
/* Merge defaults and options, without modifying defaults */
var settings = $.extend({}, defaults, options);
// The content of settings variable is now the following:
// {validate: true, limit: 5, name: "bar"}
// The 'defaults' and 'options' variables remained the same.
The Harmony ECMAScript 2015 (ES6) specifies Object.assign which will do this.
Object.assign(obj1, obj2);
Current browser support is getting better, but if you're developing for browsers that don't have support, you can use a polyfill.
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