如何匹配字符开头没有的字符串？

Question

I have an array of strings and I need to perform a search and replace on them using JavaScript. The issue is they only need to be found when they are not preceeded by one of two characters. What I have tried is:

 var searchString = new RegExp( "(?<![#\|])" + tableName,"");
 if(theLine.search(searchString) != -1){do something;}

tableName is variable and changes for each call based on data retreived from a database.

If tableName is Fred, I want to find Fred but not #Fred or |Fred.

What I have doesn't work and I'm not sure why. It's probably a simple goof but I don't see it.

Answer 1

JavaScript regex engine doesn't support lookbehinds . But you can do something like this regex to overcome that issue:

var s = 'If tableName is Fred, I want to find Fred but not #Fred or |Fred';
var r = s.replace(/([#|]Fred)|Fred/g, '$1')
//=> If tableName is , I want to find  but not #Fred or |Fred

Answer 2

var s = 'If tableName is Fred, I want to find Fred but not #Fred or |Fred';
s.match(/[^#\|]Fred/g)
[" Fred", " Fred"]

Though my answer contains an Extra Space. You need to do is

var s = 'If tableName is Fred, I want to find TFred Fred but not #Fred or |Fred';

var replaceWith = "XXXX";
s.replace(/[^#\|]Fred/g, function($1) {
    if($1 != $1.trim()) {
        return " " + replaceWith;
    } else {
        return replaceWith;
    }
})

//output - "If tableName is XXXX, I want to find XXXX XXXX but not #Fred or |Fred"

Answer 3

var searchString = new RegExp("(?<![^\|\#])" + tableName,"");
if (theLine.search(searchString) != -1){do something;}

You forgot to negate the character range that you don't want it to match on.