Type Error in javascript: Cannot read Property of undefined

Question

I have a javascript function that loos like this :

var usedNums= new Array(76);
function setSquare(thisSquare)
{

    var currSquare = "square"+ thisSquare;
    var colPlace =  new Array(0,1,2,3,4,0,1,2,3,4,0,1,2,3,4,0,1,2,3,4,0,1,2,3,4);
    var colBasis = colPlace[thisSquare] * 15;

    var newNum;
    do{
      newNum = colBasis + getNewNum() + 1;

    }while(usedNums[newNum]); //UnCaught TypeError here

    usedNums[newNum] = true;
    document.getElementById(currSquare).innerHTML = newNum;
}

The error says:

Can not read property '5' of undefined.

I have checked using console.log statement and all the variables above are getting expected values .

I understand what Type Error is but not sure where is it breaking.

**Edit:**Here is the complete Script:

window.onload = new newCard;
var usedNums= new Array(76);

function newCard()
{
  if(document.getElementById){
      for(var i =0; i<24;i++)
      { 
          console.log("Value of I is " + i);
          setSquare(i);

      }
  }else{

   alert("Sorry, your browser does not support this script");
  }
}

function setSquare(thisSquare)
{
    console.log("thissquare" + thisSquare);
    var currSquare = "square"+ thisSquare;
    console.log("currsquare" + currSquare);
    var colPlace =  new Array(0,1,2,3,4,0,1,2,3,4,0,1,2,3,4,0,1,2,3,4,0,1,2,3,4);
    console.log("colplace" + colPlace);
    var colBasis = colPlace[thisSquare] * 15;
    console.log("colbasis"+ colBasis);
    var newNum;
    do{
      newNum = colBasis + getNewNum() + 1;
      console.log("new nUM" + newNum);
    }while(usedNums[newNum]);

    usedNums[newNum] = true;
    document.getElementById(currSquare).innerHTML = newNum;
}

function getNewNum()
{
var a = Math.floor(Math.random() * 15);
console.log("random number" + a);
return a;
}

Answer 1

This line:

window.onload = new newCard;

is:

1. Invoking newCard as a constructor (which it isn't)
2. Assigning the object created from it to onload

Since you are invoking newCard there, it runs before you reach the next line:

var usedNums= new Array(76);

So usedNums is undefined when you try to read from it.

You need to assign the newCard function as your load handler. So don't invoke it:

window.onload = newCard;