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JavaScript Callback Functions in JavaScript Callbacks and the DOM Callbacks with Arguments

Make sirens?

Okay, so how would I make this into a bunch of flashing lights?

const div1 = document.getElementById('first');
const div2 = document.getElementById('second');
const div3 = document.getElementById('third');

function makeRed(element) {
    element.style.backgroundColor = "red";

function makeWhite(element) {
    element.style.backgroundColor = 'white';

function makeBlue(element) {
    element.style.backgroundColor = "blue";

function addStyleToElement(element, callback) {
Steven Parker
Steven Parker
221,293 Points

This is just a few support routines, none of which are being called. Did you mean to post a more complete project including some HTML componen(s)? If possible, make a snapshot of your workspace and post the link to it here.

2 Answers

Steven Parker
Steven Parker
221,293 Points

One way to make things "flash" is to use CSS animation to change the opacity over time, and it requires no JavaScript. For example, the following code will make anything that has the class "blink" appear and disappear every second:

.blink {
  animation: blink 1s linear infinite;
@keyframes blink {
   50% { opacity: 1 }
   51% { opacity: 0 }
  100% { opacity: 0 }

Okay I see. I was figuring you could just create a function with timeInterval to switch the divs colors every second. This is from the callback functions lesson. I am a little confused on how to proceed with a function using the above code I pasted.


Steven Parker
Steven Parker
221,293 Points

Switching colors is a job for JavaScript anyway. Here's a sample function that uses your code:

function switchColors(element) {
    setInterval(function () {
        if (element.style.backgroundColor == "red")
        else if (element.style.backgroundColor == "white")
    }, 1000);

I added a makeFlash function to the video's workspace in this snapshot that uses setInterval