_.deepExtend

A deep extend implementation for underscore, lodash and their (AFAIK non-existent) friends.

Based conceptually on the _.extend() function in underscore.js.

Copyright (C) 2012 Kurt Milam - http://xioup.com

License: MIT

Original source: https://gist.github.com/1868955

Installation:

npm install underscore-deep-extend

Dependency:

One of

• underscore.js
• lodash.js
• another clone that provides _.each and _.is(Array|Date|Null|Object|String|Undefined).

Usage:

Load it, either as is (in the browser), as an AMD module, or as a CommonJS/Node.js module), then mix it in with the parent library (which must be explicitly injected):

_.mixin({deepExtend: underscoreDeepExtend(_)});

Call it like this:

var myObj = _.deepExtend(grandparent, child, grandchild, greatgrandchild)

Notes:

Keep it DRY.

This function is especially useful if you're working with JSON config documents. It allows you to create a default config document with the most common settings, then override those settings for specific cases. It accepts any number of objects as arguments, giving you fine-grained control over your config document hierarchy.

Special Features and Considerations:

• parentRE allows you to concatenate strings. example:

  var obj = _.deepExtend({url: "www.example.com"}, {url: "http://#{_}/path/to/file.html"});
      
  console.log(obj.url);

  output: http://www.example.com/path/to/file.html

• parentRE also acts as a placeholder, which can be useful when you need to change one value in an array, while leaving the others untouched. example:

  var arr = _.deepExtend([100,    {id: 1234}, true,  "foo",  [250, 500]],
                         ["#{_}", "#{_}",     false, "#{_}", "#{_}"]);
  console.log(arr);

  output: [100, {id: 1234}, false, "foo", [250, 500]]

• The previous example can also be written like this:

  var arr = _.deepExtend([100,    {id:1234},   true,  "foo",  [250, 500]],
                        ["#{_}", {},          false, "#{_}", []]);
  console.log(arr);

  output: [100, {id: 1234}, false, "foo", [250, 500]]

• And also like this:

  var arr = _.deepExtend([100,    {id:1234},   true,  "foo",  [250, 500]],
                         ["#{_}", {},          false]);
  console.log(arr);

  output: [100, {id: 1234}, false, "foo", [250, 500]]

• Array order is important. example:

  var arr = _.deepExtend([1, 2, 3, 4], [1, 4, 3, 2]);
  console.log(arr);

  output: [1, 4, 3, 2]

• You can remove an array element set in a parent object by setting the same index value to null in a child object. Example:

  var obj = _.deepExtend({arr: [1, 2, 3, 4]}, {arr: ["#{_}", null]});
  console.log(obj.arr);

  output: [1, 3, 4]