面向对象的JavaScript-005-Function.prototype.call()的3种作用

 // call的3种作用

     // 1.Using call to chain constructors for an object

     function Product(name, price) {

       this.name = name;

       this.price = price;

       if (price < 0) {

         throw RangeError('Cannot create product ' +

                           this.name + ' with a negative price');

       }

     }

     function Food(name, price) {

       Product.call(this, name, price);

       this.category = 'food';

     }

     function Toy(name, price) {

       Product.call(this, name, price);

       this.category = 'toy';

     }

     var cheese = new Food('feta', 5);

     console.log(cheese);

     var fun = new Toy('robot', 40);

     console.log(fun);

     // 2.Using call to invoke an anonymous function

     var animals = [

       { species: 'Lion', name: 'King' },

       { species: 'Whale', name: 'Fail' }

     ];

     for (var i = 0; i < animals.length; i++) {

       (function(i) {

         this.print = function() {

           console.log('#' + i + ' ' + this.species

                       + ': ' + this.name);

         }

         this.print();

       }).call(animals[i], i);

     }

     // Using call to invoke a function and specifying the context for 'this'

     // In below example, when we will call greet the value of this will be bind to object i.

     function greet() {

       var reply = [this.person, 'Is An Awesome', this.role].join(' ');

       console.log(reply);

     }

     var i = {

       person: 'Douglas Crockford', role: 'Javascript Developer'

     };

     greet.call(i); // Douglas Crockford Is An Awesome Javascript Developer