JavaScript的电子邮件地址正则表达式

Question

I am trying to implement a regex for an email address where the first part of the email should not exceed 64 characters and the second part after the @ symbol should not exceed 253 characters and that what I did

/^([A-Za-z0-9_\-\.]{1,64})+\@([A-Za-z0-9_\-\.]{1,253})+\.([A-Za-z]{2,4})$/

But even if the first part exceed 64 characters it is still a match which should not be the case, I am using this link to test my regex: https://regex101.com/

Can anyone please assist with this

Answer 1

There are too many quantifiers in the pattern: + after {1,64}) will repeat the parenthesized pattern 1 or more times, and it is not likely what you expect. Same with ([A-Za-z0-9_\\-\\.]{1,253})+ .

You may use

/^[\w.-]{1,64}@(?!.{254})[\w.-]+\.[A-Za-z]{2,4}$/

Details

• ^ - start of string
• [\\w.-]{1,64} - 1 to 64 letters, digits, _ , . or - chars
• @ - a @ char
• (?!.{254}) - no 254 chars to the right is allowed
• [\\w.-]+ - 1+ letters, digits, _ , . or - chars
• \\. - a dot
• [A-Za-z]{2,4} - two, three or four ASCII letters
• $ - end of string.

Answer 2

You are repeating the groups with the quantifier 1+ times.

You could omit the quantifiers (and perhaps also the groups if you don't want to use them separately or referring to them)

Note that you don't have to escape the dot in the character class.

^[A-Za-z0-9_\-.]{1,64}@[A-Za-z0-9_\-.]{1,253}\.[A-Za-z]{2,4}$

Regex demo