Regex To Allow One Comma And Not At The Start Or End Of String In Javascript

I am not very good at regex and I need 3 different regex's that follow the following rules: I need a regex that only allows one comma in string I need a regex that doesn't allow a

Solution 1:

1. Allow only one comma (put a ? behind the second comma if you want to make the comma optional):

        ^[^,]*,[^,]*$

2. Allow only one comma but none at the beginning:

        ^[^,]+,[^,]*$

3. Allow only one comma but none at the end:

        ^[^,]*,[^,]+$

[^,] means "a character that is not a comma".

Solution 2:

This regex should do the job.

^[^,]+,[^,]+$

Explanation:

[^,]+ -> Not comma at least once

, -> comma (obviously)

[^,]+ -> Not comma at least once (again)

Solution 3:

Simple string operations can handle this:

functiontestForComma(str) {
    //Comma isn't first character//Comma only exists once//Comma isn't last characterreturn str.indexOf(',') >= 1 &&
        str.lastIndexOf(',') == str.indexOf(',') &&
        str.lastIndexOf(',') != str.length - 1;
}
console.log(testForComma(','));
console.log(testForComma(', '));
console.log(testForComma(' ,'));
console.log(testForComma(' , '));
console.log(testForComma(' ,, '));

Solution 4:

simple expression is like - ^[^,]+,[^,]+$

Solution 5:

1. ^(?!.*,.*,) - this is the base regex rejecting recurrent commas.
2. ^(?!,)(?!.*,.*,) - the same base with added "no comma at the start" condition
3. ^(?!.*,.*,).*(?:[^,]|^)$ - the same base with "no comma at the end". The latter is implemented as alternation group match since lookbehinds are not available in JavaScript.

Note: all these patterns allow zero or one comma in the input. If you need strictly one comma, prepend each of them with ^(?=.*,).