replacing a variable substring in a string in javascript using regex

Question

I want to replace all oldString's in string that are surrounded by whitespace, '.' , '(' or ')' using regex.

var string = ' (y) .y   y  rye';
var oldsString = 'y';
var regex = new RegExp('([.()\s])('+oldString+')([.()\s])','g');
var newString = 'x';
string = string.replace(regex, '$1'+newString+'$3');

setting regex to

var regex = new RegExp('([\.\(\)\s])('+oldString+')([\.\(\)\s])','g');

according to this website both methods should work: http://regex101.com/r/mM4xJ2 but when i try the code in node it only sets string to

' (x) .y   y  rye'

not

' (x) .x   x  rye'

tenub · Accepted Answer · 2014-03-29 01:17:28Z

1

You need to double escape since you're compiling concatenated strings with a variable to a RegExp object:

var string = ' (y) .y   y  rye';
var oldString = 'y';
var regex = new RegExp('([.()\\s])('+oldString+')([.()\\s])','g');
var newString = 'x';
string = string.replace(regex, '$1'+newString+'$3');

This returns correctly:

' (x) .x   x  rye'

answered Mar 29, 2014 at 1:17

tenub

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3 Comments

fejese Over a year ago

It fails if 2 y is separated by 1 [.()\\s], eg. ` y.y `

tenub Over a year ago

If the string is ` y.y ` you cannot have a character match twice with RegEx since the first match ` y.` consumes the . prefix from the latter substring portion .y , so the correct result should be " x.y " as opposed to " x.x " despite all common sense.

fejese Over a year ago

... and since js regex does not support lookbehind you can't do it with it this simply. I'm just pointing out so the questioner would know.

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