How to add a onclick event to an element using javascript

Question

I have created an element using document.getElementsByClassname, and would like to add a onclick event to this element, so that when someone clicks on this element onclick f

Answer 1

Please try the following:

var rows = 3;
var cols = 3;
var defaultVal=0;
var mainDiv=document.getElementById("mainDiv")
var arr = []
for (var i = 0; i < rows; i++) {
    arr[i] = [];
  for(var j=0;j