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

1.

 // 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