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