$.extend()的实现源码 --（源码学习1）

目标：

$.extend({

        add:function(a,b){

            return a + b;

        }

    })

console.log($.add(1,2));

 

是怎么实现可以将add函数挂在jQuery后面?

 

jQuery -v1.12.4

 jQuery.extend = jQuery.fn.extend = function() {
     var src, copyIsArray, copy, name, options, clone,
         target = arguments[ 0 ] || {},
         i = 1,
         length = arguments.length,
         deep = false;

     // Handle a deep copy situation
     if ( typeof target === "boolean" ) {
         deep = target;

         // skip the boolean and the target
         target = arguments[ i ] || {};
         i++;
     }

     // Handle case when target is a string or something (possible in deep copy)
     if ( typeof target !== "object" && !jQuery.isFunction( target ) ) {
         target = {};
     }

     // extend jQuery itself if only one argument is passed
     if ( i === length ) {
         target = this;
         i--;
     }

     for ( ; i < length; i++ ) {

         // Only deal with non-null/undefined values
         if ( ( options = arguments[ i ] ) != null ) {

             // Extend the base object
             for ( name in options ) {
                 src = target[ name ];
                 copy = options[ name ];

                 // Prevent never-ending loop
                 if ( target === copy ) {
                     continue;
                 }

                 // Recurse if we're merging plain objects or arrays
                 if ( deep && copy && ( jQuery.isPlainObject( copy ) ||
                     ( copyIsArray = jQuery.isArray( copy ) ) ) ) {

                     if ( copyIsArray ) {
                         copyIsArray = false;
                         clone = src && jQuery.isArray( src ) ? src : [];

                     } else {
                         clone = src && jQuery.isPlainObject( src ) ? src : {};
                     }

                     // Never move original objects, clone them
                     target[ name ] = jQuery.extend( deep, clone, copy );

                 // Don't bring in undefined values
                 } else if ( copy !== undefined ) {
                     target[ name ] = copy;
                 }
             }
         }
     }

     // Return the modified object
     return target;
 };

分析：

第3行：取到函数add

第23-26行：将this也就是jquery的实例对象,function(selector, context){} 赋值给target.

第31行：将函数add赋值给options,并进行遍历。

第36行：将options = { add:function(a,b){   ... }}的函数赋值给copy.

第60行：通过target[name]=copy; 将jquery的实例添加一个属性add 就成了jQuery['add']=function (a,b){ return a+b};