Using regular expression in Javascript

Question

I need to check whether information entered are 3 character long, first one should be 0-9 second A-Z and third 0-9 again.

I have written pattern as below:

var pattern = `'^[A-Z]+[0-9]+[A-Z]$'`;
var valid = str.match(pattern);

I got confused with usage of regex for selecting, matching and replacing.

• In this case, does[A-Z] check only one character or whole string ?
• Does + separate(split?) out characters?

Answer 1

1) + matches one or more. You want exactly one

2) declare your pattern as a REGEX literal, inside forward slashes

With these two points in mind, your pattern should be

/^[A-Z][0-9][A-Z]$/

Note also you can make the pattern slightly shorter by replacing [0-9] with the \d shortcut (matches any numerical character).

3) Optionally, add the case-insensitive i flag after the final trailing slash if you want to allow either case.

4) If you want to merely test a string matches a pattern, rather than retrieve a match from it, use test(), not match() - it's more efficient.

var valid = pattern.test(str); //true or false

Answer 2

+ means one or more characters so a possible String would be ABCD1234EF or A3B, invalid is 3B or A 6B

• Manse: the + symbol without being highlighted as code creates a list !

Answer 3

This is the regex you need :

^[0-9][A-Z][0-9]$

In this case, does[A-Z] check only one character or whole string ?

It's just check 1 char but a char can be many times in a string..

you should add ^ and $ in order to match the whole string like I did.

Does + separate(split?) out characters? no.

+ sign just shows that a chars can repeat 1+ times.

Answer 4

"+" means one or more. In your case you should use exact quantity match:

/^\w{1}\d{1}\w{1}$/