underscore.js

(c) 2010 Jeremy Ashkenas, DocumentCloud Inc.
Underscore is freely distributable under the terms of the MIT license.
Portions of Underscore are inspired by or borrowed from Prototype.js,
Oliver Steele's Functional, and John Resig's Micro-Templating.
For all details and documentation:
http://documentcloud.github.com/underscore
(function() {

Baseline setup

Establish the root object, window in the browser, or global on the server.

  var root = this;

Save the previous value of the _ variable.

  var previousUnderscore = root._;

Establish the object that gets thrown to break out of a loop iteration.

  var breaker = typeof StopIteration !== 'undefined' ? StopIteration : '__break__';

Quick regexp-escaping function, because JS doesn't have a RegExp.escape().

  var escapeRegExp = function(s) { return s.replace(/([.*+?^${}()|[\]\/\\])/g, '\\$1'); };

Save bytes in the minified (but not gzipped) version:

  var ArrayProto = Array.prototype, ObjProto = Object.prototype;

Create quick reference variables for speed access to core prototypes.

  var slice                 = ArrayProto.slice,
      unshift               = ArrayProto.unshift,
      toString              = ObjProto.toString,
      hasOwnProperty        = ObjProto.hasOwnProperty,
      propertyIsEnumerable  = ObjProto.propertyIsEnumerable;

All ECMAScript 5 native function implementations that we hope to use are declared here.

  var
    nativeForEach      = ArrayProto.forEach,
    nativeMap          = ArrayProto.map,
    nativeReduce       = ArrayProto.reduce,
    nativeReduceRight  = ArrayProto.reduceRight,
    nativeFilter       = ArrayProto.filter,
    nativeEvery        = ArrayProto.every,
    nativeSome         = ArrayProto.some,
    nativeIndexOf      = ArrayProto.indexOf,
    nativeLastIndexOf  = ArrayProto.lastIndexOf,
    nativeIsArray      = Array.isArray,
    nativeKeys         = Object.keys;

Create a safe reference to the Underscore object for use below.

  var _ = function(obj) { return new wrapper(obj); };

Export the Underscore object for CommonJS.

  if (typeof exports !== 'undefined') exports._ = _;

Export Underscore to the global scope.

  root._ = _;

Current version.

  _.VERSION = '1.1.1';

Collection Functions

The cornerstone, an each implementation. Handles objects implementing forEach, arrays, and raw objects. Delegates to ECMAScript 5's native forEach if available.

  var each = _.forEach = function(obj, iterator, context) {
    try {
      if (nativeForEach && obj.forEach === nativeForEach) {
        obj.forEach(iterator, context);
      } else if (_.isNumber(obj.length)) {
        for (var i = 0, l = obj.length; i < l; i++) iterator.call(context, obj[i], i, obj);
      } else {
        for (var key in obj) {
          if (hasOwnProperty.call(obj, key)) iterator.call(context, obj[key], key, obj);
        }
      }
    } catch(e) {
      if (e != breaker) throw e;
    }
    return obj;
  };

Return the results of applying the iterator to each element. Delegates to ECMAScript 5's native map if available.

  _.map = function(obj, iterator, context) {
    if (nativeMap && obj.map === nativeMap) return obj.map(iterator, context);
    var results = [];
    each(obj, function(value, index, list) {
      results[results.length] = iterator.call(context, value, index, list);
    });
    return results;
  };

Reduce builds up a single result from a list of values, aka inject, or foldl. Delegates to ECMAScript 5's native reduce if available.

  _.reduce = function(obj, iterator, memo, context) {
    if (nativeReduce && obj.reduce === nativeReduce) {
      if (context) iterator = _.bind(iterator, context);
      return obj.reduce(iterator, memo);
    }
    each(obj, function(value, index, list) {
      memo = iterator.call(context, memo, value, index, list);
    });
    return memo;
  };

The right-associative version of reduce, also known as foldr. Uses Delegates to ECMAScript 5's native reduceRight if available.

  _.reduceRight = function(obj, iterator, memo, context) {
    if (nativeReduceRight && obj.reduceRight === nativeReduceRight) {
      if (context) iterator = _.bind(iterator, context);
      return obj.reduceRight(iterator, memo);
    }
    var reversed = _.clone(_.toArray(obj)).reverse();
    return _.reduce(reversed, iterator, memo, context);
  };

Return the first value which passes a truth test.

  _.detect = function(obj, iterator, context) {
    var result;
    each(obj, function(value, index, list) {
      if (iterator.call(context, value, index, list)) {
        result = value;
        _.breakLoop();
      }
    });
    return result;
  };

Return all the elements that pass a truth test. Delegates to ECMAScript 5's native filter if available.

  _.filter = function(obj, iterator, context) {
    if (nativeFilter && obj.filter === nativeFilter) return obj.filter(iterator, context);
    var results = [];
    each(obj, function(value, index, list) {
      if (iterator.call(context, value, index, list)) results[results.length] = value;
    });
    return results;
  };

Return all the elements for which a truth test fails.

  _.reject = function(obj, iterator, context) {
    var results = [];
    each(obj, function(value, index, list) {
      if (!iterator.call(context, value, index, list)) results[results.length] = value;
    });
    return results;
  };

Determine whether all of the elements match a truth test. Delegates to ECMAScript 5's native every if available.

  _.every = function(obj, iterator, context) {
    iterator = iterator || _.identity;
    if (nativeEvery && obj.every === nativeEvery) return obj.every(iterator, context);
    var result = true;
    each(obj, function(value, index, list) {
      if (!(result = result && iterator.call(context, value, index, list))) _.breakLoop();
    });
    return result;
  };

Determine if at least one element in the object matches a truth test. Delegates to ECMAScript 5's native some if available.

  _.some = function(obj, iterator, context) {
    iterator = iterator || _.identity;
    if (nativeSome && obj.some === nativeSome) return obj.some(iterator, context);
    var result = false;
    each(obj, function(value, index, list) {
      if (result = iterator.call(context, value, index, list)) _.breakLoop();
    });
    return result;
  };

Determine if a given value is included in the array or object using ===.

  _.include = function(obj, target) {
    if (nativeIndexOf && obj.indexOf === nativeIndexOf) return obj.indexOf(target) != -1;
    var found = false;
    each(obj, function(value) {
      if (found = value === target) _.breakLoop();
    });
    return found;
  };

Invoke a method (with arguments) on every item in a collection.

  _.invoke = function(obj, method) {
    var args = slice.call(arguments, 2);
    return _.map(obj, function(value) {
      return (method ? value[method] : value).apply(value, args);
    });
  };

Convenience version of a common use case of map: fetching a property.

  _.pluck = function(obj, key) {
    return _.map(obj, function(value){ return value[key]; });
  };

Return the maximum element or (element-based computation).

  _.max = function(obj, iterator, context) {
    if (!iterator && _.isArray(obj)) return Math.max.apply(Math, obj);
    var result = {computed : -Infinity};
    each(obj, function(value, index, list) {
      var computed = iterator ? iterator.call(context, value, index, list) : value;
      computed >= result.computed && (result = {value : value, computed : computed});
    });
    return result.value;
  };

Return the minimum element (or element-based computation).

  _.min = function(obj, iterator, context) {
    if (!iterator && _.isArray(obj)) return Math.min.apply(Math, obj);
    var result = {computed : Infinity};
    each(obj, function(value, index, list) {
      var computed = iterator ? iterator.call(context, value, index, list) : value;
      computed < result.computed && (result = {value : value, computed : computed});
    });
    return result.value;
  };

Sort the object's values by a criterion produced by an iterator.

  _.sortBy = function(obj, iterator, context) {
    return _.pluck(_.map(obj, function(value, index, list) {
      return {
        value : value,
        criteria : iterator.call(context, value, index, list)
      };
    }).sort(function(left, right) {
      var a = left.criteria, b = right.criteria;
      return a < b ? -1 : a > b ? 1 : 0;
    }), 'value');
  };

Use a comparator function to figure out at what index an object should be inserted so as to maintain order. Uses binary search.

  _.sortedIndex = function(array, obj, iterator) {
    iterator = iterator || _.identity;
    var low = 0, high = array.length;
    while (low < high) {
      var mid = (low + high) >> 1;
      iterator(array[mid]) < iterator(obj) ? low = mid + 1 : high = mid;
    }
    return low;
  };

Safely convert anything iterable into a real, live array.

  _.toArray = function(iterable) {
    if (!iterable)                return [];
    if (iterable.toArray)         return iterable.toArray();
    if (_.isArray(iterable))      return iterable;
    if (_.isArguments(iterable))  return slice.call(iterable);
    return _.values(iterable);
  };

Return the number of elements in an object.

  _.size = function(obj) {
    return _.toArray(obj).length;
  };

Array Functions

Get the first element of an array. Passing n will return the first N values in the array. Aliased as head. The guard check allows it to work with _.map.

  _.first = function(array, n, guard) {
    return n && !guard ? slice.call(array, 0, n) : array[0];
  };

Returns everything but the first entry of the array. Aliased as tail. Especially useful on the arguments object. Passing an index will return the rest of the values in the array from that index onward. The guard check allows it to work with _.map.

  _.rest = function(array, index, guard) {
    return slice.call(array, _.isUndefined(index) || guard ? 1 : index);
  };

Get the last element of an array.

  _.last = function(array) {
    return array[array.length - 1];
  };

Trim out all falsy values from an array.

  _.compact = function(array) {
    return _.filter(array, function(value){ return !!value; });
  };

Return a completely flattened version of an array.

  _.flatten = function(array) {
    return _.reduce(array, function(memo, value) {
      if (_.isArray(value)) return memo.concat(_.flatten(value));
      memo[memo.length] = value;
      return memo;
    }, []);
  };

Return a version of the array that does not contain the specified value(s).

  _.without = function(array) {
    var values = slice.call(arguments, 1);
    return _.filter(array, function(value){ return !_.include(values, value); });
  };

Produce a duplicate-free version of the array. If the array has already been sorted, you have the option of using a faster algorithm.

  _.uniq = function(array, isSorted) {
    return _.reduce(array, function(memo, el, i) {
      if (0 == i || (isSorted === true ? _.last(memo) != el : !_.include(memo, el))) memo[memo.length] = el;
      return memo;
    }, []);
  };

Produce an array that contains every item shared between all the passed-in arrays.

  _.intersect = function(array) {
    var rest = slice.call(arguments, 1);
    return _.filter(_.uniq(array), function(item) {
      return _.every(rest, function(other) {
        return _.indexOf(other, item) >= 0;
      });
    });
  };

Zip together multiple lists into a single array -- elements that share an index go together.

  _.zip = function() {
    var args = slice.call(arguments);
    var length = _.max(_.pluck(args, 'length'));
    var results = new Array(length);
    for (var i = 0; i < length; i++) results[i] = _.pluck(args, "" + i);
    return results;
  };

If the browser doesn't supply us with indexOf (I'm looking at you, MSIE), we need this function. Return the position of the first occurence of an item in an array, or -1 if the item is not included in the array. Delegates to ECMAScript 5's native indexOf if available.

  _.indexOf = function(array, item) {
    if (nativeIndexOf && array.indexOf === nativeIndexOf) return array.indexOf(item);
    for (var i = 0, l = array.length; i < l; i++) if (array[i] === item) return i;
    return -1;
  };

Delegates to ECMAScript 5's native lastIndexOf if available.

  _.lastIndexOf = function(array, item) {
    if (nativeLastIndexOf && array.lastIndexOf === nativeLastIndexOf) return array.lastIndexOf(item);
    var i = array.length;
    while (i--) if (array[i] === item) return i;
    return -1;
  };

Generate an integer Array containing an arithmetic progression. A port of the native Python range() function. See the Python documentation.

  _.range = function(start, stop, step) {
    var a     = slice.call(arguments);
    var solo  = a.length <= 1;
    var start = solo ? 0 : a[0], stop = solo ? a[0] : a[1], step = a[2] || 1;
    var len   = Math.ceil((stop - start) / step);
    if (len <= 0) return [];
    var range = new Array(len);
    for (var i = start, idx = 0; true; i += step) {
      if ((step > 0 ? i - stop : stop - i) >= 0) return range;
      range[idx++] = i;
    }
  };

Function Functions

Create a function bound to a given object (assigning this, and arguments, optionally). Binding with arguments is also known as curry.

  _.bind = function(func, obj) {
    var args = slice.call(arguments, 2);
    return function() {
      return func.apply(obj || {}, args.concat(slice.call(arguments)));
    };
  };

Bind all of an object's methods to that object. Useful for ensuring that all callbacks defined on an object belong to it.

  _.bindAll = function(obj) {
    var funcs = slice.call(arguments, 1);
    if (funcs.length == 0) funcs = _.functions(obj);
    each(funcs, function(f) { obj[f] = _.bind(obj[f], obj); });
    return obj;
  };

Memoize an expensive function by storing its results.

  _.memoize = function(func, hasher) {
    var memo = {};
    hasher = hasher || _.identity;
    return function() {
      var key = hasher.apply(this, arguments);
      return key in memo ? memo[key] : (memo[key] = func.apply(this, arguments));
    };
  };

Delays a function for the given number of milliseconds, and then calls it with the arguments supplied.

  _.delay = function(func, wait) {
    var args = slice.call(arguments, 2);
    return setTimeout(function(){ return func.apply(func, args); }, wait);
  };

Defers a function, scheduling it to run after the current call stack has cleared.

  _.defer = function(func) {
    return _.delay.apply(_, [func, 1].concat(slice.call(arguments, 1)));
  };

Returns the first function passed as an argument to the second, allowing you to adjust arguments, run code before and after, and conditionally execute the original function.

  _.wrap = function(func, wrapper) {
    return function() {
      var args = [func].concat(slice.call(arguments));
      return wrapper.apply(wrapper, args);
    };
  };

Returns a function that is the composition of a list of functions, each consuming the return value of the function that follows.

  _.compose = function() {
    var funcs = slice.call(arguments);
    return function() {
      var args = slice.call(arguments);
      for (var i=funcs.length-1; i >= 0; i--) {
        args = [funcs[i].apply(this, args)];
      }
      return args[0];
    };
  };

Object Functions

Retrieve the names of an object's properties. Delegates to ECMAScript 5's native Object.keys

  _.keys = nativeKeys || function(obj) {
    if (_.isArray(obj)) return _.range(0, obj.length);
    var keys = [];
    for (var key in obj) if (hasOwnProperty.call(obj, key)) keys[keys.length] = key;
    return keys;
  };

Retrieve the values of an object's properties.

  _.values = function(obj) {
    return _.map(obj, _.identity);
  };

Return a sorted list of the function names available on the object.

  _.functions = function(obj) {
    return _.filter(_.keys(obj), function(key){ return _.isFunction(obj[key]); }).sort();
  };

Extend a given object with all the properties in passed-in object(s).

  _.extend = function(obj) {
    each(slice.call(arguments, 1), function(source) {
      for (var prop in source) obj[prop] = source[prop];
    });
    return obj;
  };

Create a (shallow-cloned) duplicate of an object.

  _.clone = function(obj) {
    if (_.isArray(obj)) return obj.slice(0);
    return _.extend({}, obj);
  };

Invokes interceptor with the obj, and then returns obj. The primary purpose of this method is to "tap into" a method chain, in order to perform operations on intermediate results within the chain.

  _.tap = function(obj, interceptor) {
    interceptor(obj);
    return obj;
  };

Perform a deep comparison to check if two objects are equal.

  _.isEqual = function(a, b) {

Check object identity.

    if (a === b) return true;

Different types?

    var atype = typeof(a), btype = typeof(b);
    if (atype != btype) return false;

Basic equality test (watch out for coercions).

    if (a == b) return true;

One is falsy and the other truthy.

    if ((!a && b) || (a && !b)) return false;

One of them implements an isEqual()?

    if (a.isEqual) return a.isEqual(b);

Check dates' integer values.

    if (_.isDate(a) && _.isDate(b)) return a.getTime() === b.getTime();

Both are NaN?

    if (_.isNaN(a) && _.isNaN(b)) return false;

Compare regular expressions.

    if (_.isRegExp(a) && _.isRegExp(b))
      return a.source     === b.source &&
             a.global     === b.global &&
             a.ignoreCase === b.ignoreCase &&
             a.multiline  === b.multiline;

If a is not an object by this point, we can't handle it.

    if (atype !== 'object') return false;

Check for different array lengths before comparing contents.

    if (a.length && (a.length !== b.length)) return false;

Nothing else worked, deep compare the contents.

    var aKeys = _.keys(a), bKeys = _.keys(b);

Different object sizes?

    if (aKeys.length != bKeys.length) return false;

Recursive comparison of contents.

    for (var key in a) if (!(key in b) || !_.isEqual(a[key], b[key])) return false;
    return true;
  };

Is a given array or object empty?

  _.isEmpty = function(obj) {
    if (_.isArray(obj) || _.isString(obj)) return obj.length === 0;
    for (var key in obj) if (hasOwnProperty.call(obj, key)) return false;
    return true;
  };

Is a given value a DOM element?

  _.isElement = function(obj) {
    return !!(obj && obj.nodeType == 1);
  };

Is a given value an array? Delegates to ECMA5's native Array.isArray

  _.isArray = nativeIsArray || function(obj) {
    return !!(obj && obj.concat && obj.unshift && !obj.callee);
  };

Is a given variable an arguments object?

  _.isArguments = function(obj) {
    return !!(obj && obj.callee);
  };

Is a given value a function?

  _.isFunction = function(obj) {
    return !!(obj && obj.constructor && obj.call && obj.apply);
  };

Is a given value a string?

  _.isString = function(obj) {
    return !!(obj === '' || (obj && obj.charCodeAt && obj.substr));
  };

Is a given value a number?

  _.isNumber = function(obj) {
    return (obj === +obj) || (toString.call(obj) === '[object Number]');
  };

Is a given value a boolean?

  _.isBoolean = function(obj) {
    return obj === true || obj === false;
  };

Is a given value a date?

  _.isDate = function(obj) {
    return !!(obj && obj.getTimezoneOffset && obj.setUTCFullYear);
  };

Is the given value a regular expression?

  _.isRegExp = function(obj) {
    return !!(obj && obj.test && obj.exec && (obj.ignoreCase || obj.ignoreCase === false));
  };

Is the given value NaN -- this one is interesting. NaN != NaN, and isNaN(undefined) == true, so we make sure it's a number first.

  _.isNaN = function(obj) {
    return _.isNumber(obj) && isNaN(obj);
  };

Is a given value equal to null?

  _.isNull = function(obj) {
    return obj === null;
  };

Is a given variable undefined?

  _.isUndefined = function(obj) {
    return typeof obj == 'undefined';
  };

Utility Functions

Run Underscore.js in noConflict mode, returning the _ variable to its previous owner. Returns a reference to the Underscore object.

  _.noConflict = function() {
    root._ = previousUnderscore;
    return this;
  };

Keep the identity function around for default iterators.

  _.identity = function(value) {
    return value;
  };

Run a function n times.

  _.times = function (n, iterator, context) {
    for (var i = 0; i < n; i++) iterator.call(context, i);
  };

Break out of the middle of an iteration.

  _.breakLoop = function() {
    throw breaker;
  };

Add your own custom functions to the Underscore object, ensuring that they're correctly added to the OOP wrapper as well.

  _.mixin = function(obj) {
    each(_.functions(obj), function(name){
      addToWrapper(name, _[name] = obj[name]);
    });
  };

Generate a unique integer id (unique within the entire client session). Useful for temporary DOM ids.

  var idCounter = 0;
  _.uniqueId = function(prefix) {
    var id = idCounter++;
    return prefix ? prefix + id : id;
  };

By default, Underscore uses ERB-style template delimiters, change the following template settings to use alternative delimiters.

  _.templateSettings = {
    evaluate    : /<%([\s\S]+?)%>/g,
    interpolate : /<%=([\s\S]+?)%>/g
  };

JavaScript micro-templating, similar to John Resig's implementation. Underscore templating handles arbitrary delimiters, preserves whitespace, and correctly escapes quotes within interpolated code.

  _.template = function(str, data) {
    var c  = _.templateSettings;
    var tmpl = 'var __p=[],print=function(){__p.push.apply(__p,arguments);};' +
      'with(obj||{}){__p.push(\'' +
      str.replace(/'/g, "\\'")
         .replace(c.interpolate, function(match, code) {
           return "'," + code.replace(/\\'/g, "'") + ",'";
         })
         .replace(c.evaluate || null, function(match, code) {
           return "');" + code.replace(/\\'/g, "'")
                              .replace(/[\r\n\t]/g, ' ') + "__p.push('";
         })
         .replace(/\r/g, '\\r')
         .replace(/\n/g, '\\n')
         .replace(/\t/g, '\\t')
         + "');}return __p.join('');";
    var func = new Function('obj', tmpl);
    return data ? func(data) : func;
  };

Aliases:

  _.each     = _.forEach;
  _.foldl    = _.inject       = _.reduce;
  _.foldr    = _.reduceRight;
  _.select   = _.filter;
  _.all      = _.every;
  _.any      = _.some;
  _.contains = _.include;
  _.head     = _.first;
  _.tail     = _.rest;
  _.methods  = _.functions;

The OOP Wrapper

If Underscore is called as a function, it returns a wrapped object that can be used OO-style. This wrapper holds altered versions of all the underscore functions. Wrapped objects may be chained.

  var wrapper = function(obj) { this._wrapped = obj; };

Helper function to continue chaining intermediate results.

  var result = function(obj, chain) {
    return chain ? _(obj).chain() : obj;
  };

A method to easily add functions to the OOP wrapper.

  var addToWrapper = function(name, func) {
    wrapper.prototype[name] = function() {
      var args = slice.call(arguments);
      unshift.call(args, this._wrapped);
      return result(func.apply(_, args), this._chain);
    };
  };

Add all of the Underscore functions to the wrapper object.

  _.mixin(_);

Add all mutator Array functions to the wrapper.

  each(['pop', 'push', 'reverse', 'shift', 'sort', 'splice', 'unshift'], function(name) {
    var method = ArrayProto[name];
    wrapper.prototype[name] = function() {
      method.apply(this._wrapped, arguments);
      return result(this._wrapped, this._chain);
    };
  });

Add all accessor Array functions to the wrapper.

  each(['concat', 'join', 'slice'], function(name) {
    var method = ArrayProto[name];
    wrapper.prototype[name] = function() {
      return result(method.apply(this._wrapped, arguments), this._chain);
    };
  });

Start chaining a wrapped Underscore object.

  wrapper.prototype.chain = function() {
    this._chain = true;
    return this;
  };

Extracts the result from a wrapped and chained object.

  wrapper.prototype.value = function() {
    return this._wrapped;
  };

})();