bind _.bind(function, object, *arguments)
Bind a function to an object, meaning that whenever the function is called, the value of this will be the object. Optionally, pass arguments to the function to pre-fill them, also known as partial application. For partial application without context binding, use partial.
var func = function(greeting){ return greeting + ': ' + this.name };
func = _.bind(func, {name: 'moe'}, 'hi');
func();
=> 'hi: moe'
bindAll _.bindAll(object, *methodNames)
Binds a number of methods on the object, specified by methodNames, to be run in the context of that object whenever they are invoked. Very handy for binding functions that are going to be used as event handlers, which would otherwise be invoked with a fairly useless this. methodNames are required.
var buttonView = {
label : 'underscore',
onClick: function(){ alert('clicked: ' + this.label); },
onHover: function(){ console.log('hovering: ' + this.label); }
};
_.bindAll(buttonView, 'onClick', 'onHover');
// When the button is clicked, this.label will have the correct value.
jQuery('#underscore_button').on('click', buttonView.onClick);
partial _.partial(function, *arguments)
Partially apply a function by filling in any number of its arguments, without changing its dynamic this value. A close cousin of bind. You may pass _ in your list of arguments to specify an argument that should not be pre-filled, but left open to supply at call-time. Note: if you need _ placeholders and a this binding at the same time, use both _.partial and _.bind.
var subtract = function(a, b) { return b - a; };
sub5 = _.partial(subtract, 5);
sub5(20);
=> 15
// Using a placeholder
subFrom20 = _.partial(subtract, _, 20);
subFrom20(5);
=> 15
memoize _.memoize(function, [hashFunction])
Memoizes a given function by caching the computed result. Useful for speeding up slow-running computations. If passed an optional hashFunction, it will be used to compute the hash key for storing the result, based on the arguments to the original function. The default hashFunction just uses the first argument to the memoized function as the key. The cache of memoized values is available as the cache property on the returned function.
var fibonacci = _.memoize(function(n) {
return n < 2 ? n: fibonacci(n - 1) + fibonacci(n - 2);
});
delay _.delay(function, wait, *arguments)
Much like setTimeout, invokes function after wait milliseconds. If you pass the optional arguments, they will be forwarded on to the function when it is invoked.
var log = _.bind(console.log, console);
_.delay(log, 1000, 'logged later');
=> 'logged later' // Appears after one second.
once _.once(function)
Creates a version of the function that can only be called one time. Repeated calls to the modified function will have no effect, returning the value from the original call. Useful for initialization functions, instead of having to set a boolean flag and then check it later.
var initialize = _.once(createApplication);
initialize();
initialize();
// Application is only created once.
after _.after(count, function)
Creates a wrapper of function that does nothing at first. From the count-th call onwards, it starts actually calling function. Useful for grouping asynchronous responses, where you want to be sure that all the async calls have finished, before proceeding.
var renderNotes = _.after(notes.length, render);
_.each(notes, function(note) {
note.asyncSave({success: renderNotes});
});
// renderNotes is run once, after all notes have saved.
before _.before(count, function)
Creates a wrapper of function that memoizes its return value. From the count-th call onwards, the memoized result of the last invocation is returned immediately instead of invoking function again. So the wrapper will invoke function at most count - 1 times.
var monthlyMeeting = _.before(3, askForRaise);
monthlyMeeting();
monthlyMeeting();
monthlyMeeting();
// the result of any subsequent calls is the same as the second call
wrap _.wrap(function, wrapper)
Wraps the first function inside of the wrapper function, passing it as the first argument. This allows the wrapper to execute code before and after the function runs, adjust the arguments, and execute it conditionally.
var hello = function(name) { return "hello: " + name; };
hello = _.wrap(hello, function(func) {
return "before, " + func("moe") + ", after";
});
hello();
=> 'before, hello: moe, after'
negate _.negate(predicate)
Returns a new negated version of the predicate function.
var isFalsy = _.negate(Boolean);
_.find([-2, -1, 0, 1, 2], isFalsy);
=> 0
compose _.compose(*functions)
Returns the composition of a list of functions, where each function consumes the return value of the function that follows. In math terms, composing the functions f(), g(), and h() produces f(g(h())).
var greet = function(name){ return "hi: " + name; };
var exclaim = function(statement){ return statement.toUpperCase() + "!"; };
var welcome = _.compose(greet, exclaim);
welcome('moe');
=> 'hi: MOE!'
