Detailed explanation of JavaScript substr() string interception function_Basic knowledge

substr Definition and Usage The
substr() method can extract the specified number of characters starting from the start subscript in a string.

Syntax
stringObject.substr(start,length)

参数	描述
start	必需。要抽取的子串的起始下标。必须是数值。如果是负数，那么该参数声明从字符串的尾部开始算起的位置。也就是说，-1 指字符串中最后一个字符，-2 指倒数第二个字符，以此类推。
length	可选。子串中的字符数。必须是数值。如果省略了该参数，那么返回从 stringObject 的开始位置到结尾的字串。

Description
If length is 0 or negative, an empty string will be returned. If this parameter is not specified, the substring will be continued to the end of stringvar.

Example
The following example demonstrates the use of the substr method.

The first character to intercept the string.

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The result is: j

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It means interception Starting from the 12th character in the string, the length is 5

In this example we will use substr() to extract some characters from a string:

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Output:

lo world!

Example 2

In this example we will use substr() to extract some characters from a string:

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Output:

lo worl