Question

I’m trying to translate a PHP class into JavaScript. The only thing I’m having trouble with is getting an item out of an array variable. I’ve created a simple jsfiddle here. I cannot figure out why it won’t work.

(EDIT: I updated this code to better reflect what I’m doing. Sorry for the previous mistake.)

function tattooEightBall() {

this.subjects = ['a bear', 'a tiger', 'a sailor'];

this.prediction = make_prediction();

var that = this;



function array_random_pick(somearray) {
      //return array[array_rand(array)];
      var length = somearray.length;

      var random = somearray[Math.floor(Math.random()*somearray.length)];
    return random;


}


function make_prediction() {

    var prediction = array_random_pick(this.subjects);
    return prediction;
}

}
var test = tattooEightBall();
document.write(test.prediction);

​

Answer 1

Works fine here, you are simple not calling

classname();

After you define the function.

Update

When you make a call to *make_prediction* , this will not be in scope. You are right on the money creating a that variable, use it on *make_prediction* :

var that = this;

this.prediction = make_prediction();

function make_prediction() {
  var prediction = ''; //initialize it

  prediction = prediction + array_random_pick(that.subjects);
  return prediction;
}

You can see a working version here: http://jsfiddle.net/zKcpC/

This is actually pretty complex and I believe someone with more experience in Javascript may be able to clarify the situation.

Edit2: Douglas Crockfords explains it with these words:

By convention, we make a private that variable. This is used to make
the object available to the private methods. This is a workaround for
an error in the ECMAScript Language Specification which causes this to
be set incorrectly for inner functions.

To see the complete article head to: http://javascript.crockford.com/private.html