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October 02, 2017, at 07:50 AM

I was attempting to place a circle on an HTML canvas that measured 1920 * 850 on (x, y) where x varied by 50 and y varied by 75. I set up a nested for loop to accomplish this but soon found it was not working, i.e. the loop stopped after a certain point. I then did some scenarios with simple nested for loops without the circle placement code and found that they were also stopping after a certain point.

In the code below, I have a simple nested for loop and upon running it, it stops when i = 14 and j = 19. In the console, it just states 'An error has occurred in the Javascript console

for (var i = 0; i < 20; i++) { 
  j = 0 
  for (var j = 0; j < 70; j++) { 
    console.log('i: ' + i + ' j: ' + j); 

Is there something fundamentally wrong here, this seems like such a simple piece of code but I do not know why it would stop.

Any ideas?

Answer 1

I have solved the issue, sort of. I found a post where the console log was not showing the output of a for loop after 999. Additionally, there was an error in my initial javascript loop to produce the circles, I did not use a beginPath after each circle was drawn and that was giving very messed up results.

I.E. Console log with for loop

After reviewing this I realized my code might still be running but the console is not showing it. So I rewrote the code to fill the canvas as I had started out to and it is working now.

$(document).ready(function ()
    var header = $('#header');
    var footer = $('#footer');
    var canvas = $('#myCanvas3')[0];
    canvas.width = window.innerWidth;
    canvas.height = window.innerHeight - header.height() - footer.height();
    var ctx = canvas.getContext('2d');

    var i = 0;
    var j = 0;
    for (var y = 1; y < 18; y++)
            i = y * 50;
            for (var x = 0; x < canvas.width; x++)
                j += 1;
                if (j == 50) {
                    console.log('x: ' + x);
                    ctx.fillStyle = 'red';
                    ctx.arc(x, i, 2, 0, Math.PI * 2, false);
                    j = 0;

Lesson learned - when drawing items on the canvas make sure to use a beginPath when drawing a new item!!

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