Why does this JavaScript Regex match an underscore?

Question

I am trying to use following JavaScript RE to match the string where allowed characters are uppercase or lowercase letters, digits, hypens (-), and periods (.). The underscore "_" is not allowed:

pattern = /^([a-zA-z0-9\-\.]+)$/

But when I run the test in the Chrome console: pattern.test("_linux");

The result is true, but should be false according to our rules. What's the reason?

Note: . doesn't have to be escaped inside the character class. — Felix Kling
– Felix Kling, Commented Aug 12, 2016 at 1:59
in Page 149 from the book <JavaScript The Definitive Guide> 4th edition, "." has special meaning and it should be preceded with "\". But I tested in the Chrome it works correctly if you don't add "\". For the "-" it's not needed. For the convenience of the programmer, is it best to add "\" if you don't know whether it should add "\" or not? — flashstar
– flashstar, Commented Aug 12, 2016 at 16:43

rvighne · Accepted Answer · 2016-08-12 01:34:35Z

9

In your regex, you have written A-z (with a lowercase z at the end). In the JavaScript regex engine, this translates to character codes 65 to 122 rather than the desired 65 to 90. And the underscore character is within this range (char code 95); see an ASCII chart. Change it to a capital Z, making your regex:

^([a-zA-Z0-9\-\.]+)$

edited Aug 12, 2016 at 1:34

answered Aug 12, 2016 at 1:27

rvighne

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1 Comment

flashstar Over a year ago

I made a careless mistake. Thank you a lot!

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