Extend

[trans]

Why "without extending any of the built-in JavaScript objects" ?

[jashkenas]

Because extending built-ins is often makes your code incompatible with other libraries and scripts. If you want to extend built ins, because you're certain that your JS is going to be run in isolation, I suggest taking a look at Prototype.js, which provides many of the same helpers as Underscore, in a more object-oriented fasion.

But Prototype is also a good example of how extending native objects can bite you -- in previous versions of Prototype, and Array#reduce function was added to the native Array object. ECMAScript 5 standardized a version of Array#reduce, a couple years later, and browsers implemented it as a native function. Unfortunately, JavaScript's reduce isn't compatible with Prototype's reduce, and any page that loads those versions of Prototype will monkey-patch the native version of the function out of existence...

[trans]

Sure. I understand the hazards, but it could be an option. If one knows it won't be an issue it sure can be convenient.

Also, there is another way to avoid these issues buy still extend the built-in: using a single access method, e.g. in this case maybe _ could work.

[]._.reduce()

[jashkenas]

If you'd like to extend Array.prototype with the Underscore methods, feel free to add them yourself...

// Underscore methods that we want to implement on Array.
var methods = ['each', 'map', 'reduce', 'reduceRight', 'detect', 'select',
  'reject', 'all', 'any', 'include', 'invoke', 'pluck', 'max', 'min', 'sortBy',
  'sortedIndex', 'toArray', 'size', 'first', 'rest', 'last', 'without',
  'indexOf', 'lastIndexOf', 'isEmpty'];

// Mix in each method as a proxy.
_.each(methods, function(method) {
  Array.prototype[method] = function() {
    return _[method].apply(_, [this].concat(_.toArray(arguments)));
  };
});

[trans]

Nice. Thanks.