$.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};