write regex for everything except a particular pattern for password in javascript -

i'm using following regex pattern validating password.

var expression = /^[^\!\@\#\$\%\^\&\*\(\)\-\s\=\+\[\{\]\}\;\:\'\"\<\>\?\/\,\.\`\~\'][^\s]+$/ 

and it's working fine.

now need change in such way can give characters allowed or blocked on top of this.

i tried following code not working.

var blockchar = "t"; var allowchar = "b";      var expression = '^' + blockchar + '[^\!\@\#\$\%\^\&\*\(\)\-\s\=\+\[\{\]\}\;\:\'\"\<\>\?\/\,\.\`\~\'' + allowchar + '][^\s]+$' var regexp = new regexp(expression); var elmval = document.getelementbyid("txt1").value; if (!elmval.match(regexp)) {     return "validation failed"; } 

can guide me on how incorporate 2 variables (blockchar , allowchar) in this? values in blockchar should blocked , value in allowchar should allowed.

you have different ways allow or forbid characters in string. lets see 3 basic examples:

• example 1: give allowed characters in character class

  /^[a-za-z0-9@]+$/

here, letters, numbers , arobase allowed, anchors @ begining , @ end ensure whole string must match pattern.

• example 2: give unwanted characters in character class (using negated character class [^.....])

  /^[^&#='")(]+$/

all characters allowed except & # = ' "

• example 3: check if string contain unwanted character

  /[&#='")(]/

if result of match false , string length not null (or size want), string valid.

how allow new characters:

with example 1, it's easy, put in character class:

var charclass = 'a-za-z0-9@'; var allowchars = '{}'; var regexp = new regexp('^[' + charclass + allowchars + ']+$'); 

with example 2, more difficult because removing character class not easy. way use alternation:

var charclass = '[^&#=\'")(]'; var allowchars = '&#'; var regexp = new regexp('^(?:' + charclass + '|[' + allowchars + '])+$'); 

with example 3, same problem example 2, need remove characters class. can use negative lookahead instead before class:

var charclass = '[^&#=\'")(]'; var allowchars = '&#'; var regexp = new regexp('^(?![' + allowchars + '])' + charclass ); 

how forbid characters:

example 1: don't touch original class add negative lookahead (not followed by):

var charclass = '[a-za-z0-9@]+'; var blockchars = 'yz8'; var regexp = new regexp('^(?!.*[' + blockchars + '])' + charclass + '$'); 

characters y z 8 in character class, negative lookahead make pattern fail if 1 these present in string.

example 2:

you can use same precedant trick, or can add forbidden characters (negated) character class:

var charclass = '^&#=\'")('; var blockchars = 'yz8'; var regexp = new regexp('^[' + charclass + blockchars + ']+$'); 

example 3: can add characters directly @ end of class too.

with these examples, can build code allow characters , forbid other characters dynamically:

example 1:

var charclass = 'a-za-z0-9@'; var allowchars = '{}'; var blockchars = 'yz8'; var regexp = new regexp('^(?!.*[' + blockchars + '])[' + charclass + allowchars + ']+$'); 

example 2:

var charclass = '^&#=\'")('; var allowchars = '&#'; var blockchars = 'yz8'; var regexp = new regexp('^(?:[' + charclass + blockchars + ']|[' + allowchars + '])+$'); 

example 3:

var charclass = '^&#=\'")('; var allowchars = '&#'; var blockchars = 'yz8'; var regexp = new regexp('^(?![' + allowchars + '])[' + charclass + blockchars + ']');