如何在Javascript类中从“私有方法”访问“公共变量”

Question

First, See my code plz.

function test(){

    this.item = 'string';

    this.exec = function(){
        something();
    }

    function something(){
        console.log(this.item);
        console.log('string');
    }
}

And I made class and call 'exec function', like this code

var t = new test();

t.exec();

But result is...

undefined
string

I wanna access from something function to test.item.

Have you any solution?

Answer 1

You need to call something with apply so that this is properly set inside of something :

function test(){

    this.item = 'string';

    this.exec = function(){
        something.apply(this);
    }

    function something(){
        console.log(this.item);
        console.log('string');
    }
}

As @aaronfay pointed out, this happens because this doesn't refer to the object that new test() created. You can read more about it here , but the general rule is:

If a function is invoked on an object , then this refers to that object . If a function is invoked on its own (as is the case in your code), then this refers to the global object, which in the browser is window .

Answer 2

You have many choices, but I recommend the last one.

var item = 'string'

or

this.exec = function(){
    something.apply(this, []);
}

or

var that = this;
function something(){
    console.log(that.item);
    console.log('string');
}

Answer 3

this.item in something() isn't what you think it is.

The this value is different. In this case, it's the global object.

The best solution, in my opinion, is to declare a variable with a reference to this , that can be accessed inside the inner function.

---

function test() {
    var that = this; // a reference to 'this'

    function something() {
        console.log(that.item); // using the outer 'this'
        console.log('string');
    }

    this.item = 'string';

    this.exec = function(){
        something();
    }
}

Answer 4

Why not just define something like this:

Fiddle

function test(){

    this.item = 'string';

    this.exec = function(){
        this.something();
    }

    this.something = function(){
        console.log(this.item);
        console.log('string');
    }
} 

var t = new test();
t.exec();
// output:
// string 
// string