just-extend

What is just-extend?

The just-extend npm package is a utility library for deep or shallow copying and extending of objects. It allows users to merge properties from source objects into a target object, with the option to perform deep (recursive) merges.

What are just-extend's main functionalities?

Shallow extend

This feature allows the user to merge properties from one or more source objects into a target object. If the same property exists in both objects, the value from the last object will be used.

{"var extend = require('just-extend');
var obj1 = {a: 3, b: 4};
var obj2 = {b: 5, c: 6};
var result = extend(obj1, obj2);
// result is {a: 3, b: 5, c: 6}"}

Deep extend

This feature allows the user to perform a deep merge, where nested objects are also merged together. This is useful when you want to combine objects with nested structures.

{"var extend = require('just-extend');
var obj1 = {a: {b: 3}};
var obj2 = {a: {c: 4}};
var result = extend(true, obj1, obj2);
// result is {a: {b: 3, c: 4}}"}

Extend with customizer function

This feature allows the user to provide a customizer function that determines how values are merged. The customizer function can be used to specify custom merging behavior for specific properties or types of values.

{"var extend = require('just-extend');
var customizer = function(objValue, srcValue) {
  if (Array.isArray(objValue)) {
    return objValue.concat(srcValue);
  }
};
var obj1 = {a: [1, 2], b: 3};
var obj2 = {a: [3, 4], b: 4};
var result = extend(customizer, obj1, obj2);
// result is {a: [1, 2, 3, 4], b: 4}"}

Other packages similar to just-extend

lodash.merge

Lodash's merge function is similar to just-extend's deep extend feature. It allows for deep merging of objects, but lodash is a larger utility library with many additional functions, which might not be needed if only object merging is required.

object-assign

The object-assign package provides a polyfill for the Object.assign method, which performs a shallow merge of objects. It is similar to just-extend's shallow extend feature but does not support deep merging.

deepmerge

Deepmerge is another package that offers deep merging of objects. It is similar to just-extend's deep extend feature but provides more options for customizing the behavior of the merge, such as array concatenation and overwriting of properties.

README

just-extend

Part of a library of zero-dependency npm modules that do just do one thing.
Guilt-free utilities for every occasion.

Try it now

import extend from 'just-extend';

let obj = {a: 3, b: 5};
extend(obj, {a: 4, c: 8}); // {a: 4, b: 5, c: 8}
obj; // {a: 4, b: 5, c: 8}

let obj = {a: 3, b: 5};
extend({}, obj, {a: 4, c: 8}); // {a: 4, b: 5, c: 8}
obj; // {a: 3, b: 5}

let arr = [1, 2, 3];
let obj = {a: 3, b: 5};
extend(obj, {c: arr}); // {a: 3, b: 5, c: [1, 2, 3]}
arr.push[4];
obj; // {a: 3, b: 5, c: [1, 2, 3, 4]}

let arr = [1, 2, 3];
let obj = {a: 3, b: 5};
extend(true, obj, {c: arr}); // {a: 3, b: 5, c: [1, 2, 3]}
arr.push[4];
obj; // {a: 3, b: 5, c: [1, 2, 3]}

extend({a: 4, b: 5}); // {a: 4, b: 5}
extend(3, {a: 4, b: 5}); // throws
extend({a: 4, b: 5}, 3); // throws
extend({a: 4, b: 5}, {b: 4, c: 5}, 'c'); // throws