YUI学习笔记（一） : Yahoo global object 翻译

本文介绍了Yahooglobalobject的基础使用方法，包括如何引入yahoo.js文件，利用YAHOO.namespace进行命名空间的创建，避免全局变量污染。此外，还详细讲解了YAHOO.lang提供的各种实用函数，如类型检测、继承机制等。

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简介

Yahoo global object 提供namespace机制和封装了一些好用的方法. js名称为yahoo.js ,使用YUI前必须先引入这个js,且应该最先加载.

源文件

< script type ="text/javascript" src ="http://yui.yahooapis.com/2.6.0/build/yahoo/yahoo-min.js" ></ script >

常用方法列举如下:

YAHOO.namespace

避免js全局变量污染的好办法,用法如下:

// Creates a namespace for "myproduct1"
YAHOO.namespace ( " myproduct1 " );
YAHOO.myproduct1.Class1 = function (info) {
alert(info);
};

// Creates a namespace for "myproduct2", and for "mysubproject1"
YAHOO.namespace ( " myproduct2.mysubproject1 " );
YAHOO.myproduct2.mysubproject1.Class1 = function (info) {
alert(info);
};

YAHOO.lang

提供了一些简便易用方法,如下:

// true, an array literal is an array
YAHOO.lang.isArray([ 1 , 2 ]);

// false, an object literal is not an array
YAHOO.lang.isArray({ " one " : " two " });

// however, when declared as an array, it is true
function () {
     var a = new Array();
    a[ " one " ] = " two " ;
     return YAHOO.lang.isArray(a);
}();

// false, a collection of elements is like an array, but isn't
YAHOO.lang.isArray(document.getElementsByTagName( " body " ));

// true, false is a boolean
YAHOO.lang.isBoolean( false );

// false, 1 and the string "true" are not booleans
YAHOO.lang.isBoolean( 1 );
YAHOO.lang.isBoolean( " true " );

// null is null, but false, undefined and "" are not
YAHOO.lang.isNull( null ); // true
YAHOO.lang.isNull(undefined); // false
YAHOO.lang.isNull( "" ); // false

// a function is a function, but an object is not
YAHOO.lang.isFunction( function (){}); // true
YAHOO.lang.isFunction({foo: " bar " }); // false

// true, ints and floats are numbers
YAHOO.lang.isNumber( 0 );
YAHOO.lang.isNumber( 123.123 );

// false, strings that can be cast to numbers aren't really numbers
YAHOO.lang.isNumber( " 123.123 " );

// false, undefined numbers and infinity are not numbers we want to use
YAHOO.lang.isNumber( 1 / 0 );

// true, objects, functions, and arrays are objects
YAHOO.lang.isObject({});
YAHOO.lang.isObject( function (){});
YAHOO.lang.isObject([ 1 , 2 ]);

// false, primitives are not objects
YAHOO.lang.isObject( 1 );
YAHOO.lang.isObject( true );
YAHOO.lang.isObject( " {} " );

// strings
YAHOO.lang.isString( " {} " ); // true
YAHOO.lang.isString({foo: " bar " }); // false
YAHOO.lang.isString( 123 ); // false
YAHOO.lang.isString( true ); // false

// undefined is undefined, but null and false are not
YAHOO.lang.isUndefined(undefined); // true
YAHOO.lang.isUndefined( false ); // false
YAHOO.lang.isUndefined( null ); // false

YAHOO.lang.hasOwnProperty

检查某个对象是否有某属性

// this is what we are protecting against
Object.prototype.myCustomFunction = function (x) {
    alert(x);
}

var o = {};
o[ " foo " ] = " bar " ;
o[ " marco " ] = " polo " ;

// this is where we need the protection
for ( var i in o) {
     if (YAHOO.lang.hasOwnProperty(o, i)) {
        alert( " good key: " + i);
    } else {
        alert( " bad key: " + i);
    }
}

YAHOO.lang.extend

提供了继承机制.(译者注:js使用继承还是有一定风险,建议酌情使用.)

YAHOO.namespace( " test " );

YAHOO.test.Class1 = function (info) {
    alert( " Class1: " + info);
};

YAHOO.test.Class1.prototype.testMethod = function (info) {
    alert( " Class1: " + info);
};

YAHOO.test.Class2 = function (info) {
     // chain the constructors
    YAHOO.test.Class2.superclass.constructor.call( this , info);
    alert( " Class2: " + info);
};

// Class2 extends Class1.  Must be done immediately after the Class2 constructor
YAHOO.lang.extend(YAHOO.test.Class2, YAHOO.test.Class1);

YAHOO.test.Class2.prototype.testMethod = function (info) {
     // chain the method
    YAHOO.test.Class2.superclass.testMethod.call( this , info);
    alert( " Class2: " + info);
};

var class2Instance = new YAHOO.test.Class2( " constructor executed " );
class2Instance.testMethod( " testMethod invoked " );

YAHOO.lang.augment

将某个对象的prototype属性复制到另一个对象,代码重用的好方法.

< div id = " consoleelement " > </ div >

< script >
// //////////////////////////////////////////////////////////////////////////
// The ConsoleProvider example will log to the console if available, or a
// div with id="consoleelement" if the console is not available
// //////////////////////////////////////////////////////////////////////////
YAHOO.example.ConsoleProvider = function () { };
YAHOO.example.ConsoleProvider.prototype = {
    log: function (msg) {
         // use the error console if available (FF+FireBug or Safari)
         if ( typeof console != " undefined " ) {
            console.log(msg);
         // write the msg to a well-known div element
        } else {
             var el = document.getElementById( " consoleelement " );
             if (el) {
                el.innerHTML += " <p> " + msg + " </p> " ;
            }
        }
    }
};

// //////////////////////////////////////////////////////////////////////////
// Define a class that should be able to write debug messages
// //////////////////////////////////////////////////////////////////////////
YAHOO.example.ClassWithLogging = function () { };
YAHOO.lang.augment(YAHOO.example.ClassWithLogging, YAHOO.example.ConsoleProvider);

// //////////////////////////////////////////////////////////////////////////
// Try it out
// //////////////////////////////////////////////////////////////////////////
var c = new YAHOO.example.ClassWithLogging();
c.log( " worked " );

</ script >