I asked this question to answer it because there is no clear info or question about this. I found the solution in a comment, not in an answer. so I hope this will help others.
HTML
<html lang="en">
<head>
<meta charset="UTF-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Document</title>
</head>
<body>
<a href="" class="btn" id="btn" onclick="clickBtn()">btn</a>
<div class="box" id="box"></div>
</body>
</html>
CSS
.btn{
width: 150px;
height: 50px;
cursor: pointer;
margin: 10px;
background: black;
color: white;
}
.box{
width: 200px;
height: 200px;
background: orange;
margin: 5px;
}
javascript
var box = document.getElementById("box");
function clickBtn() {
if (box.style.background = "orange"){
box.style.background = "blue";
} else {
box.style.background = "green";
}
}
1- If you use <a> as a button, it will refresh the page as long as it has href="". so remove href and it will work without refreshing the page.
2- if you want to keep the href, then change the <a> to button. it worked for me.
use href="javascript:void(0)" in a tag. The javascript:void(0) can be used when we don't want to refresh or load a new page in the browser on clicking a hyperlink.