javascript中的call()，它可以用来调用所有者对象作为参数的方法，通过 call()，您能够使用属于另一个对象的方法。

var person = {
  fullName: function() {
    return this.firstName + " " + this.lastName;
  }
}
var person1 = {
  firstName:"Bill",
  lastName: "Gates"
}
var person2 = {
  firstName:"Steve",
  lastName: "Jobs"
}
person.fullName.call(person2);  //打印结果是"Steve Jobs"

以上案例总结 作用一：call()可以调用某一函数

var person = {
  fullName: function(city, country) {
    console.log(this)
    return this.firstName + " " + this.lastName + "," + city + "," + country;
  }
}
var person1 = {
  firstName:"Bill",
  lastName: "Gates"
}
var person2 = {
  firstName:"Steve",
  lastName: "Jobs"
}
person.fullName.call()  //这样调用this指向window
person.fullName.call(person1) //这样调用this指向person1这个对象

以上案例总结 作用二：call()可以这个函数的this指向。

另外，call()也可以接受参数，比如：

var person = {
  fullName: function(city, country) {
    console.log(this)
    return this.firstName + " " + this.lastName + "," + city + "," + country;
  }
}
var person1 = {
  firstName:"Bill",
  lastName: "Gates"
}
var person2 = {
  firstName:"Steve",
  lastName: "Jobs"
}
person.fullName.call(person1,'CHINA','BeiJing') //打印结果为"Bill Gates,CHINA,BeiJing"