用javascript编写正则表达式的最佳方法是什么？

Question

Good day!

I don't know regular expressions very well, but I tried to compose one. I need this regular expression matched a record for example:

The user enters any value in the text field that can start with 00x00 and end with 12x99 , it must contain only the sign "x" and the first pair of numbers (the one before "x") must not exceed the number "12" .

I tried a record like this:

/^(00|01|02|03|04|05|06|07|08|09|10|11|12)x([0-9]{2,2})&/

and it fits me, but it's too long expression, I'm sure there's something shorter. Asking for help from You !

Answer 1

You can shorten the expression quite a bit.

^(0\d|1[0-2])x\d{2}$

First you can remove the parenthesis around the entire expression, they are not required if you want a full match.

The you can replace every [0-9] block with the \\d token.

Then the quantifier can be simplified if you want a strict quantity {2,2} to {2}

The first part is a bit more tricky. You can actually separate the match in 2 parts. You need to match every number from 00 to 09 , and every number from 10 to 12 .

So this is exactly what we are going to do.

First the match from 00 to 09 , the first digit doesn't change, so that's easy. The second digit is a full range from 0 to 9, so we use \\d as previously mentioned. That gives us 0\\d .

The second half has the same fixed first digit, 1. Again that's easy. Then it's actually a shortened range from 0 to 2. That gives us 1[0-2] .

Could be one or the other, so we encapsulate that part and use the | (or) token.

And that's it, we combine everything and get the expression above!