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
1 jQuery.extend = jQuery.fn.extend = function() { 2 var src, copyIsArray, copy, name, options, clone, 3 target = arguments[ 0 ] || {}, 4 i = 1, 5 length = arguments.length, 6 deep = false; 7 8 // Handle a deep copy situation 9 if ( typeof target === "boolean" ) {10 deep = target;11 12 // skip the boolean and the target13 target = arguments[ i ] || {};14 i++;15 }16 17 // Handle case when target is a string or something (possible in deep copy)18 if ( typeof target !== "object" && !jQuery.isFunction( target ) ) {19 target = {};20 }21 22 // extend jQuery itself if only one argument is passed23 if ( i === length ) {24 target = this;25 i--;26 }27 28 for ( ; i < length; i++ ) {29 30 // Only deal with non-null/undefined values31 if ( ( options = arguments[ i ] ) != null ) {32 33 // Extend the base object34 for ( name in options ) {35 src = target[ name ];36 copy = options[ name ];37 38 // Prevent never-ending loop39 if ( target === copy ) {40 continue;41 }42 43 // Recurse if we're merging plain objects or arrays44 if ( deep && copy && ( jQuery.isPlainObject( copy ) ||45 ( copyIsArray = jQuery.isArray( copy ) ) ) ) {46 47 if ( copyIsArray ) {48 copyIsArray = false;49 clone = src && jQuery.isArray( src ) ? src : [];50 51 } else {52 clone = src && jQuery.isPlainObject( src ) ? src : {};53 }54 55 // Never move original objects, clone them56 target[ name ] = jQuery.extend( deep, clone, copy );57 58 // Don't bring in undefined values59 } else if ( copy !== undefined ) {60 target[ name ] = copy;61 }62 }63 }64 }65 66 // Return the modified object67 return target;68 }; 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};