The problem of replacing replace function in JavaScript

Today, my colleague asked me a question about the substitution of JavaScript, and he had a string "</SheetItems><ElectricalStatus>" and wanted to use "!" To replace the "<", using the Replace function but found that only the first "<" can be replaced.

Such as:

<script language="javascript">
var str="</SheetItems><ElectricalStatus>";
str=str.replace("<","!");
alert(str);
</script>

Found the data to find that the use of regular expressions can solve this problem

<script language="javascript">
var str="</SheetItems><ElectricalStatus>";
str=str.replace(/\</g,"!");
alert(str);
</script>

There are several types of regular expressions here, such as "/[<]/g" or "/\</g" or "/</g" can be achieved.