jquery基礎（七）

Utility Methods

jQuery offers several utility methods in the $ namespace. These methods are helpful for accomplishing routine programming tasks. Below are examples of a few of the utility methods; for a complete reference on jQuery utility methods, visit http://api.jquery.com/category/utilities/.

$.trim

Removes leading and trailing whitespace.

$.trim('    lots of extra whitespace    ');
// returns 'lots of extra whitespace'

$.each

Iterates over arrays and objects.

$.each([ 'foo', 'bar', 'baz' ], function(idx, val) {
    console.log('element ' + idx + 'is ' + val);
});

$.each({ foo : 'bar', baz : 'bim' }, function(k, v) {
    console.log(k + ' : ' + v);
});

Note

There is also a method $.fn.each, which is used for iterating over a selection of elements.

$.inArray

Returns a value's index in an array, or -1 if the value is not in the array.

var myArray = [ 1, 2, 3, 5 ];

if ($.inArray(4, myArray) !== -1) {
    console.log('found it!');
}

$.extend

Changes the properties of the first object using the properties of subsequent objects.

var firstObject = { foo : 'bar', a : 'b' };
var secondObject = { foo : 'baz' };

var newObject = $.extend(firstObject, secondObject);
console.log(firstObject.foo); // 'baz'
console.log(newObject.foo);   // 'baz'

If you don't want to change any of the objects you pass to $.extend, pass an empty object as the first argument.

var firstObject = { foo : 'bar', a : 'b' };
var secondObject = { foo : 'baz' };

var newObject = $.extend({}, firstObject, secondObject);
console.log(firstObject.foo); // 'bar'
console.log(newObject.foo);   // 'baz'

$.proxy

Returns a function that will always run in the provided scope — that is, sets the meaning of thisinside the passed function to the second argument.

var myFunction = function() { console.log(this); };
var myObject = { foo : 'bar' };

myFunction(); // logs window object

var myProxyFunction = $.proxy(myFunction, myObject);
myProxyFunction(); // logs myObject object

If you have an object with methods, you can pass the object and the name of a method to return a function that will always run in the scope of the object.

var myObject = {
    myFn : function() {
        console.log(this);
    }
};

$('#foo').click(myObject.myFn); // logs DOM element #foo
$('#foo').click($.proxy(myObject, 'myFn')); // logs myObject

Checking types

As mentioned in the "JavaScript basics" section, jQuery offers a few basic utility methods for determining the type of a specific value.

Example 4.1. Checking the type of an arbitrary value

var myValue = [1, 2, 3];

// Using JavaScript's typeof operator to test for primative types
typeof myValue == 'string'; // false
typeof myValue == 'number'; // false
typeof myValue == 'undefined'; // false
typeof myValue == 'boolean'; // false

// Using strict equality operator to check for null
myValue === null; // false

// Using jQuery's methods to check for non-primative types
jQuery.isFunction(myValue); // false
jQuery.isPlainObject(myValue); // false
jQuery.isArray(myValue); // true