Uncaught TypeError: Cannot read property '0' of undefined in 3d array

Question

Following is my Code:

        var i,j;
        var period = 5;
        var sec = new Array(new Array(new Array()));
        for(i=0;i<6;i++){
            for(j=1;j<period;j++){  
                sec[j][i][j] = j;
                console.log("SEC: "+j+i+j+" = "+sec[j][i][j]);
                console.log('/n');
            }
        }

When I execute the above code I get cannot read property '0' of undefined at sec[j][i][j] assignment. I don't understand the reason behind it.. It would be great if you guys can help me on this. Thanks in advance.

Answer 1

That is because sec[1][0][1] is undefined, you need to push an array every time

  var i,j, period = 6; var sec = []; for(i=0;i<6;i++){ for(j=1;j<period;j++){ sec[j] = []; sec[j][i] = []; sec[j][i][j] = j; console.log("SEC: "+j+i+j+" = "+sec[j][i][j]); console.log('/n'); } } 

Answer 2

var sec = new Array(new Array(new Array()));

Doesn't do what you think it does. Try to allocate the inner arrays when needed like this instead

var i, j;
var period = 5;
var sec = [];
for (i = 0; i < 6; i++) {
  for (j = 1; j < period; j++) {
    sec[j] = sec[j] || [];
    sec[j][i] = sec[j][i] || [];
    sec[j][i][j] = j;
    console.log("SEC: " + j + i + j + " = " + sec[j][i][j]);
    console.log('\n');
  }
}

Also, /n prints '/n' not a new line which is \\n

Answer 3

Although you have declared array as 3D array, JavaScript do not allocate the memory to it.

So being 3D array sec[0] is undefined.