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Jackson Monk
4,527 PointsAnyone know why setInterval() only runs once?
Trying to create a slow gravity effect on a CSS circle with JS. However, the circle only moves once instead of every 500 milliseconds like I tell it to in setInterval(). Why is this?
<html>
<head>
<style>
.circle {
position: relative;
padding: 15px;
background-color: black;
border-radius: 50%;
width: 0.2%;
}
</style>
</head>
<body>
<div class = circle></div>
<script>
let circle = document.getElementsByTagName('div')[0];
function fall(rate) {
circle.style.top += rate;
}
function execute() {
fall(2);
}
setInterval(execute, 500);
</script>
</body>
</html>
1 Answer
![Steven Parker](https://uploads.teamtreehouse.com/production/profile-photos/969492/micro_tool_chess_set_2.jpg)
Steven Parker
230,688 PointsThe interval is running, but you don't see any effect because the property value is a string and you need to convert it to a number to do math with it:
function fall(rate) {
var top = parseInt(circle.style.top || 0) + rate;
circle.style.top = top + "px";
}
Jackson Monk
4,527 PointsJackson Monk
4,527 PointsI thought I tried that, but I thought it was weird because it ran once, and if it wasn't working it wouldn't run at all. I'll try this though
Jackson Monk
4,527 PointsJackson Monk
4,527 PointsWow! Works perfectly! Why is it that when I tried it with
parseInt(circle.style.top)
, it didn't work, but when I didparseInt(circle.style.top || 0)
, it worked perfectly?Steven Parker
230,688 PointsSteven Parker
230,688 PointsThat's because until you assign it, that property returns only an empty string. But the "
|| 0
" will substitute a zero when the string is empty.Happy coding!