HTML and CSS Reference
In-Depth Information
Some of the most common and helpful methods are documented in the following list.
_.each(list, callback, [context]) : Calls back each element of the list as an argument to
the callback. It uses the native forEach in the browsers that support it. Notice _.each takes an addi-
tional “context” object that is bound to this inside the callback., callback, [context]) : Similar to _.each , except it takes the return values
from the callback method and returns a new array.
_.find(list, callback, [context]) : Returns the first item in the list for which the callback
function returns true . It's useful for finding an element in a list based on some arbitrary criteria func-
_.filter(list, callback, [context]) : Similar to _.find except that it returns an array
of all the items for which the callback returns true .
_.without(array, [*values]) : Returns a new array without any instances of values removed;
useful, for example, for removing dead sprites from a list.
_.uniq(array, [isSorted], [iterator]) : _.uniq returns a copy of an array with any
duplicate elements removed. If the array happens to be in a sorted state, pass true to isSorted to
improve performance.
Taken together, these methods make working with lists of objects much more concise.
Using Utility Functions
Underscore also provides a number of general utility functions that can make your life easier.
_.bindAll(object, [*methodNames]) : Modifies any calls to methodNames on object so
that the context is always object . This means you can pass methods to jQuery event handlers, for ex-
ample, without needing to worry about the context of this .
_.keys(object) / _.values(object) : Returns all of an object's keys or values.
_.extend(destination, *sources) : Copies all the properties from a list of source objects
over to the destination, overwriting any existing properties.[ObjectType] : Underscore.js provides a good number of methods of the form[Ob-
jectType] to check the type of a passed-in object. This is useful because JavaScript doesn't provide
built-in type checking methods. The methods Underscore provides are _.isEqual , _.isEmpty ,
_.isElement, _.isArray , _.isFunction , _.isString , _ isNumber , _.isBoolean ,
_.isNaN , _.isNull , and _.isUndefined. All the[ObjectType] methods are relatively
self-explanatory: They each check the type of the object passed in and return true or false . They
provide a succinct way to do type checking on JavaScript objects, which is useful for checking arguments
and faking polymorphism by having methods behave differently depending on what is passed into them.
_.uniqueId([prefix]) : Generates a globally unique identifier for client-side DOM elements or
models. This is useful because you often want to add unique ID attributes to elements you add to the
These utility methods, particularly _.extend are used frequently in the topic.
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