regex - Regular Expression for javascript to validate name and version -

i trying write regular expression in javascript. need validate name , version, following conditions:

name:

version:

name

the regex

^(?! )((?!  )(?! $)[a-za-z ]){3,50}$

only alphabets, no numbers , special characters => use character class that
```
[a-za-z] 
```
no trailing spaces @ start or end, , no multiple spaces between words. => "anchoring" regex should thing on line , can't partially match. negative lookahead more 2 spaces not allowed
```
^...$ (?!  ) 
```
no spaces @ beginning , and end => again can use lookaround
```
^(?! )...(?<! )$ 
```
but since javascript doesn't support lookbehind have use lookahead
```
(?! $)[a-za-z ] 
```
minimum of 3 , maximum of 50 characters.
```
{3,50} 
```

version

the regex

^\d{1,2}\.\d{1,2}\.\d{1,2}$

format should [number].[number].[number]
```
\d+\.\d+\.\d+ 
```
only single dot between numbers (1.3..4 invalid, 1.3.4 ok) => specifying \d digits allowed followed dot (which should escaped since otherwise mean character)
each number can of 1 or 2 digits, 1.11.26(valid), not 2.343.23 (invalid)
```
\d{1,2} 
```

the last regex becomes following in javascript

if (/^\d{1,2}\.\d{1,2}\.\d{1,2}$/.test(subject)) {     // successful match } else {     // match attempt failed }

EXC