如何为第一个字符和字符串的其余部分定义不同的正则表达式？

Question

I want to validate and process a string, which should be a telephone number. For the first character, numbers and + is accepted, for the rest, just numbers.

I have the solution to accept + and numbers, but just for the whole string:

 console.log("asd242++asf43+234".replace(/[^+\\d]/g, "")) 

But suffering from defining different check for the first character, and the rest.

Answer 1

You can use the following:

([^+\d]|(?!^)\+)

It matches everything that is not a digit nor a + and doesn't match + at the beginning of the string!
So your test log would look like this:

 console.log("+asd242++asf43+234".replace(/([^+\\d]|(?!^)\\+)/g, "")) 

(i added a + to the beginning to show it handles this correctly!)

See a Demo that shows it matches all your cases!

Answer 2

What I understood you want to validate +numbers . You should use ^ and $ in start of end of your regex. I think following regex will work if i am not wrong.

/^\+[0-9]+$/

Answer 3

Try this one: /^[+]?[0-9]+$/g

^ - start of string

[+]? - single optional + character

[0-9]+ - one or more digit

$ - end of string