Inner function cannot access outer functions variable

Question

I have created the following jsfiddle which highlights my problem. http://jsfiddle.net/UTG7U/

var ExampleObject = function() {
   var myArray = new Array();
   this.example = function() {
       alert(this.myArray);
   };
}

var exampleObj = new ExampleObject();
exampleObj.example();

I am new to JavaScript and trying to create an object, field and a method. I can't get my method to access my field variable.

It's recommended you use the array literal `[]` to create an array instead of `new Array();` — 0x499602D2, Sep 02 '12 at 19:44

score 7 · Answer 1 · answered Sep 02 '12 at 20:10

You have confused two types of variables: Local variables and member variables. var myArray is a local variable. this.myArray is a member variable.

Solution using only local variables:

var ExampleObject = function() {
   var myArray = new Array(); // create a local variable
   this.example = function() {
       alert(myArray); // access it as a local variable
   };
}

var exampleObj = new ExampleObject();
exampleObj.example();

Solution using only member variables:

var ExampleObject = function() {
   this.myArray = new Array(); // create a member variable
   this.example = function() {
       alert(this.myArray); // access it as a member variable
   };
}

var exampleObj = new ExampleObject();
exampleObj.example();

You answered this quite a while ago, but I don't think your second answer would work. In that case, 'this' is referring to the inner function, not the outer. — rjcarr, Jun 13 '13 at 00:01
Try it. It works. That's because `this` refers to "the thing before the dot" which in this case is `exampleObj`. — Raymond Chen, Jun 13 '13 at 02:57

score 6 · Accepted Answer · answered Sep 02 '12 at 19:41

you were trying to access a local variable using this operator which is wrong, so here is the working example

var ExampleObject = function() {
   var myArray = new Array(1,2,3);
   this.example = function() {
       alert(myArray);
   };
}
var exampleObj = new ExampleObject();
exampleObj.example();

Link: http://jsfiddle.net/3QN37/

score 1 · Answer 3 · answered Sep 02 '12 at 19:41

1

You don't need the this.myArray. Using myArray alone will suffice (and work).

answered Sep 02 '12 at 19:41

Rhyono

2,289
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38

score 1 · Answer 4 · edited Sep 02 '12 at 19:45

1

alert(myArray); should work fine I think

edited Sep 02 '12 at 19:45

athspk

6,576
7
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51

answered Sep 02 '12 at 19:41

SNAG

1,836
2
20
37

score 1 · Answer 5 · answered Sep 02 '12 at 19:42

What this is changes with the scope of each function. However, myArray will be visible to inner function. Example:

var ExampleObject = function() {
   var myArray = new Array();
   this.example = function() {
       alert(myArray);
   };
}
var exampleObj = new ExampleObject();
exampleObj.example();

Inner function cannot access outer functions variable

5 Answers5

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