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Having problem with a little flashing metronome project I'm working on.

I'm using .setInterval to flash the screen between two colors and HTML buttons to increase or decrease the flash rate. The problem lies in that my variables for the increased or decreased flash rate functions call the original flash rate function and everything gets convoluted. I've tried a bunch of ways to address this and I can't get it right; too new to JS. Any thoughts?

As a secondary question if you have the time.... What would be a better approach for adjusting flash rate? Form? Drop down menu? Etc.

Here is the link to my codepen http://codepen.io/Fedreg/pen/aNJojy

Thanks for any help!!

2 Answers

29,445 Points

Hi, The problem is that you don't stop any interval, just add one after another. You need to assign interval to a variable and then you can clear interval.

var x = 500;
var flashStep = 1;
var myInterval;

function flash() {
  if (flashStep == 1) {
    document.bgColor = "#51cfff";
    flashStep = 2;
  } else {
    document.bgColor = "#333";
    flashStep = 1;

function faster() {
  myInterval = window.setInterval(flash, x -= 50);

function slower() {
  myInterval = window.setInterval(flash, x += 50);

myInterval = window.setInterval(flash, x);

Thanks akak!! I tried a solution like that but couldn't quite get it right; was over complicating it. Thanks again!