2、 Three ways to write JS code

Write JS Three ways to code

1、 Inline
Format ：

<button onclick="alert('hello js');"> Am I </button>

2、 Inside JS（ In page ）
Format ：

<!-- type="text/javascript"  Indicates that the type of script you write is JS -->
<!--  If you don't write , The default is type="text/javascript" -->
<script type="text/javascript"> alert("hello js"); </script>

Be careful ： Advice on body Bottom , Because the code is executed from top to bottom , stay head The label says JS Code can't get body The elements of the label , If you want to write in front , Think again HTML Elements in can be used window.onload.

3、 external JS（ Outer chain ）
Format ：

<script type="text/javascript" src="out.js"></script>

Be careful ： Outer chain script You cannot write in a code block js Code , Even if it's written, it won't execute ;

<script type="text/javascript" src="out.js"> alert("helo js~"); //  Will not be executed  </script>