how to send an alert in javascript

//you can either do this:

function mousePressed() {
//you can have any message
alert("I'm the best");

//or you can do this:

function keyPressed() {
//you can do any key
if (keyCode === UP_ARROW) {
//and any message
alert(number = random(0, 500));

//or you can do an (if) statement

if(x > width) {
alert("yay you did it");

Alert in JS doesn't return anything -- it just Displays Message