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【Javascript】IE下substr()函数截取末尾字符时的问题

这两天刚遇到一个问题，substr()函数在IE和FF下表现不一致，导致了一个IE下的bug。

可以通过以下代码来测试：

<script>var str = "abc"; alert(str.substr(-1, 1));</script>

提示：你可以先修改部分代码再运行。

希望得到的是c，FF下表现正常；但跑到IE下，显示abc，不是期望的结果。看来IE在处理substr()第一个参数为负数的情况处理方式不一样。

为了解决问题，另觅蹊径，改用substring()函数代替substr()





<script>var str = "abc"; var len = str.length; alert(str.substring(len - 1, len));</script>

提示：你可以先修改部分代码再运行。

p.s. 附一篇学习文章：substr() vs substring() vs slice()

substr()

substr() method extracts a specified number of characters in a string, from a start index.

Syntax: string.substr(start, length);

Quick Notes aout Substr:

• If start is negative, Internet Explorer returns the whole string. That’s wrong! IE should use the last character in the string.

substring()

substring() method extracts the chars in a string between two specified indexes.

Syntax: string.substring(start, stop);

Quick Notes about Substring:

• If start equals stop, it returns an empty string.
• If stop is omitted, it extracts characters to the end of the string.
• If either argument is less than 0 or is NaN, it is treated as if it were 0.
• If either argument is greater than string’s length, either argument will use string’s length.
• If start > stop, then substring will swap those 2 arguments

slice()

slice() works like substring() with a few different behaviors.

Syntax: string.slice(start, stop);

Quick Notes about Slice:

• If stop is omitted, slice extracted chars to the end of the string, exactly like substring().
• If start > stop, slice() will NOT swap the 2 arguments.
• If start is negative, slice() will set char from the end of string, exactly like substr() in Firefox. This behavior is observed in both Firefox and IE.
• If stop is negative, slice() will set stop to: (string.length – 1) – stop (original value).

参考：Javascript: substr() v.s. substring()




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