First we have to understand what: DOM tree
Through the following code:
<!DOCTYPE html>
<html>
<body>
<p><a id="myAnchor" href="http://www.w3school.com.cn/">W3School</a></p>
<P> Click the button to display the value of the href attribute linked above. </ P>
<Button onclick = "myFunction ()"> Try </ button>
<p id="demo"></p>
<script>
function myFunction() {
var x = document.getElementById("myAnchor").href;
document.getElementById("demo").innerHTML = x;
}
</script>
</body>
</html>
The results show a button:
w3school
Read it? If you do not know can own try.