jQuery.extend with configurable behaviour for arrays.

Well, it's actually pretty good, and is generally sufficient, but it merges arrays in a strange way depending of what you want. Example:

var DEFAULTS = {
  operators: ['AND', 'OR', 'XOR']
};

var config = {
  operators: ['OR', 'XOR']
};

config = $.extend(true, {}, DEFAULTS, config);

When executing this code, one will expects to get config.operators = ['OR', 'XOR'], but instead you get ['OR', 'XOR', 'XOR], because $.extend merges arrays like objects as per spec.

Other deep merging utilities I found either have the same behaviour or perform both merge and append on array values (nrf110/deepmerge for example).

jQuery.extendext.js contains a new $.extendext function with the exact same behaviour as $.extend if not additional config is provided.

The difference is that it accepts a optional second string argument to specify how arrays should be merged.

jQuery.extendext([deep ,][arrayMode ,] target, object1 [, objectN ] )

• deep boolean — If true, the merge becomes recursive (aka. deep copy).
• arrayMode string — Specify the arrays merge operation, either replace, concat, extend or default
• target object — The object to extend. It will receive the new properties.
• object1 object — An object containing additional properties to merge in.
• objectN object — Additional objects containing properties to merge in.

In this mode, every Array values in target is replaced by a copy of the same value found in objectN. The copy is recursive if deep is true.

var DEFAULTS = {
  operators: ['AND', 'OR', 'XOR']
};

var config = {
  operators: ['OR', 'XOR']
};

config = $.extendext(true, 'replace', {}, DEFAULTS, config);

assert.deepEqual(config, {
  operators: ['OR', 'XOR']
}) // true;

In this mode, Arrays found in both target and objectN are always concatenated. If deep is true, a recursive copy of each value if concatenated instead of the value itself.

var DEFAULTS = {
  operators: ['AND', 'OR', 'XOR']
};

var config = {
  operators: ['OR', 'XOR']
};

config = $.extendext(true, 'concat', {}, DEFAULTS, config);

assert.deepEqual(config, {
  operators: ['AND', 'OR', 'XOR', 'OR', 'XOR']
}) // true;

This is how nrf110/deepmerge works. In this mode, Arrays values are treated a bit differently:

• If plain objects are found at the same position in both target and objectN they are merged recursively or not (depending on deep option).
• Otherwise, if the value in objectN is not found in target, it is pushed at the end of the array.

var DEFAULTS = {
  operators: ['AND', 'OR', 'XOR']
};

var config = {
  operators: ['XOR', 'NAND']
};

config = $.extendext(true, 'extend', {}, DEFAULTS, config);

assert.deepEqual(config, {
  operators: ['AND', 'OR', 'XOR', 'NAND']
}) // true;

Same as $.extend.

var DEFAULTS = {
  operators: ['AND', 'OR', 'XOR']
};

var config = {
  operators: ['OR', 'XOR']
};

config = $.extendext(true, 'default', {}, DEFAULTS, config);

assert.deepEqual(config, {
  operators: ['OR', 'XOR', 'XOR']
}) // true;

A QUnit test suite is provided in tests directory.

$.extendext is tested against core jQuery tests for $.extend and nrf110/deepmerge tests (with the difference that extendext, like extend, modifies the first argument where deepmerge does not touch it).