Calling a method in a Javascript Constructor and Accessing Its Variables

Question

I am trying to call a method from the constructor of my javascript constructor, is this possible and if so, I can't seem to get it working, any insight would be great! Thanks!

function ValidateFields(pFormID){
    var aForm = document.getElementById(pFormID);
    this.errArray = new Array();//error tracker
    this.CreateErrorList();
}
/*
 * CreateErrorList()
 * Creates a list of errors:
 *   <ul id="form-errors">
 *    <li>
 *     You must provide an email.
 *    </li>
 *   </ul>
 * returns nothing
 */
 ValidateFields.prototype.CreateErrorList = function(formstatid){
     console.log("Create Error List");
 }

I got it to work with what is above, but I can't seem to access the 'errArray' variable in CreateErrorList function.

Answer 1

Yes, it is possible, when your constructor function executes, the this value has already the [[Prototype]] internal property pointing to the ValidateFields.prototype object.

Now, by looking at the your edit, the errArray variable is not available in the scope of the CreateErrorList method, since it is bound only to the scope of the constructor itself.

If you need to keep this variable private and only allow the CreateErrorList method to access it, you can define it as a privileged method , within the constructor:

function ValidateFields(pFormID){
  var aForm = document.getElementById(pFormID);
  var errArray = [];

  this.CreateErrorList = function (formstatid){
    // errArray is available here
  };
  //...
  this.CreateErrorList();
}

Note that the method, since it's bound to this , will not be shared and it will exist physically on all object instances of ValidateFields .

Another option, if you don't mind to have the errArray variable, as a public property of your object instances, you just have to assign it to the this object:

//..
this.errArray = [];
//..

More info:

• Private Members in JavaScript
• Closures

Answer 2

Solution:

function ValidateFields(pFormID){
    console.log("ValidateFields Instantiated");
    var aForm = document.getElementById(pFormID);
    this.errArray = new Array();//error tracker
    this.CreateErrorList(); //calling a constructors method
}

ValidateFields.prototype.CreateErrorList = function(){
   console.log("Create Error List");
   console.log(this.errArray); //this is how to access the constructors variable
}

Hope this helps anyone who might have a question like this in the future.

Answer 3

Are you creating an object of ValidateFields somewhere?

Edit : You need to prepend this whenever referring to a function's public properties.

Updated the code here: http://jsbin.com/afiru/edit