Underscore.js

Collections

each_.each(list, iterator, [context])
Iterates over a list of elements, yielding each in turn to an iterator function. The iterator is bound to the context object, if one is passed. If list is a Javascript object, a pair with key and value properties will be yielded. Delegates to the native forEach method if it exists.

_.each([1, 2, 3], function(num){ alert(num); });
=> alerts each number in turn...

map_.map(list, iterator, [context])
Produces a new array of values by mapping each value in list through a transformation function (iterator). If the native map method exists, it will be used instead.

_.map([1, 2, 3], function(num){ return num * 3 });
=> [3, 6, 9]

inject_.inject(list, memo, iterator, [context])
Also known as reduce and foldl, inject reduces a list of values into a single value. Memo is the initial state of the reduction, and each successive step of it should be returned by iterator.

var sum = _.inject([1, 2, 3], 0, function(memo, num){ return memo + num });
=> 6

detect_.detect(list, iterator, [context])
Looks through each value in the list, returning the first one that passes a truth test (iterator). The function returns as soon as it finds the true element, and doesn't continue to traverse the list.

var even = _.detect([1, 2, 3, 4, 5, 6], function(num){ return num % 2 == 0; });
=> 2

select_.select(list, iterator, [context])
Looks through each value in the list, returning an array of all the values that pass a truth test (iterator). Delegates to the native filter method, if it exists.

var evens = _.select([1, 2, 3, 4, 5, 6], function(num){ return num % 2 == 0; });
=> [2, 4, 6]

reject_.reject(list, iterator, [context])
Returns the values in list without the elements that the truth test (iterator) passes. The opposite of select.

var odds = _.reject([1, 2, 3, 4, 5, 6], function(num){ return num % 2 == 0; });
=> [1, 3, 5]

all_.all(list, [iterator], [context])
Returns true if all of the values in the list pass the iterator truth test. If an iterator is not provided, the truthy value of the element will be used instead. Delegates to the native method every, if present.

_.all([true, 1, null, 'yes']);
=> false

any_.any(list, iterator, [context])
Returns true if any of the values in the list pass the iterator truth test. Short-circuits and stops traversing the list if a true element is found. Delegates to the native method some, if present.

_.any([null, 0, 'yes', false]);
=> true

include_.include(list, value)
Returns true if the value is present in the list, using == to test equality. Uses indexOf internally, if list is an Array.

_.include([1, 2, 3], 3);
=> true

invoke_.invoke(list, methodName)
Calls the method named by methodName on each value in the list. Any extra arguments passed to invoke will be forwarded on to the method invocation.

_.invoke([[5, 1, 7], [3, 2, 1]], 'sort');
=> [[1, 5, 7], [1, 2, 3]]

pluck_.pluck(list, propertyName)
An optimized version of what is perhaps the most common use-case for map: returning a list of property values.

var stooges = [{name : 'moe', age : 40}, {name : 'larry', age : 50}, {name : 'curly', age : 60}];
_.pluck(stooges, 'name');
=> ["moe", "larry", "curly"]

max_.max(list, [iterator], [context])
Returns the maximum value in list. If iterator is passed, it will be used on each value to generate the criterion by which the value is ranked.

var stooges = [{name : 'moe', age : 40}, {name : 'larry', age : 50}, {name : 'curly', age : 60}];
_.max(stooges, function(stooge){ return stooge.age; });
=> {name : 'curly', age : 60};

min_.min(list, [iterator], [context])
Returns the minimum value in list. If iterator is passed, it will be used on each value to generate the criterion by which the value is ranked.

var numbers = [10, 5, 100, 2, 1000];
_.min(numbers);
=> 2

sortBy_.sortBy(list, iterator, [context])
Returns a sorted list, ranked by the results of running each value through iterator.

_.sortBy([1, 2, 3, 4, 5, 6], function(num){ return Math.sin(num); });
=> [5, 4, 6, 3, 1, 2]

sortedIndex_.sortedIndex(list, value, [iterator])
Uses a binary search to determine the index at which the value should be inserted into the list in order to maintain the list's sorted order. If an iterator is passed, it will be used to compute the sort ranking of each value.

_.sortedIndex([10, 20, 30, 40, 50], 35);
=> 3

toArray_.(list, iterator, [context])

size_.(list, iterator, [context])