About IE bugs and string interception substr Solutions _ Basics

I have not paid attention to this question, I would like to do this today:

Copy Code code as follows:

var str = ' Hello world 8024 ';

Str.substr ( -4,4);

Negative numbers are counted from the end.

should return: 8024

But found that the IE6-IE8,SUBSTR parameter does not support negative numbers, the return is: Hell, you can test.

So, we still don't recommend using this substr method.
Let's switch to the substring method.

such as: Str.substring (str.length-4);
On the correct return: 8024