First, let’s take a look at the use of the substring function.

A, the substring

A substring needs at least one parameter, the first of which is the starting position and the second, optional, is the ending position.

Only one parameter:

<meta charset="UTF-8" />
<script type='text/javascript'>
/**
 * substring Function USES DEMO
 */
var str = ' Welcome to script house ';
var sub = str.substring(3);
alert(sub); //< br / >) out: a child comes to Ben's house as a guest
</script>

Two parameters:

<meta charset="UTF-8" />
<script type='text/javascript'>
/**
 * substring Function USES DEMO
 */
var str = ' Welcome to script house ';
var sub = str.substring(3,11);
alert(sub); //< br / > out: a child to the script house
</script>

Second, the substr

Substr also requires at least one parameter, the first of which is the starting position and the second, optional, is the length.

Only one parameter:

<meta charset="UTF-8" />
<script type='text/javascript'>
/**
 * substring Function USES DEMO
 */
var str = ' Welcome to script house ';
var sub = str.substr(3);
alert(sub); //< br / >) out: a child comes to Ben's house as a guest
</script>

Two parameters:

<meta charset="UTF-8" />
<script type='text/javascript'>
/**
 * substring Function USES DEMO
 */
var str = ' Welcome to script house ';
var sub = str.substr(3,2);
alert(sub); //Out: child
</script>

From the above example, it can be seen that the result of substring and substr is the same if there is only one parameter, only the second parameter is different.