Question

I’m attempting to replace certain parts of a string with regex in JavaScript, but only if they are not wrapped within {{{ and }}}.

The system I currently have in place does multiple string replacements and wraps the replacements in these brackets. So therefore, if I was to replace “h” with the day of the week (let’s say Thursday), the replacement would output "{{{Thursday}}}". If the replacement was to happen again, the string would ultimately become "{{{T{{{Thursday}}}ursday}}}" as the “h” in Thursday has been replaced.

What I’m looking for is a regex pattern that would replace the “h” but only if it is not contained within the {{{ and }}} wrappers.

Thanks in advance 🙂

Edit:

Here is some example code. Each replacement gets wrapped in the brackets, and regex patterns use (?!{{{) and (?!}}}) in an attempt to avoid past replacements.

var string = 'n d m y',
    dayTextRegex = /(?!{{{)n(?!}}})/g,
    dayRegex = /(?!{{{)d(?!}}})/g,
    monthRegex = /(?!{{{)m(?!}}})/g,
    yearRegex = /(?!{{{)y(?!}}})/g;

string = string.replace(dayTextRegex, '{{{Monday}}}');
string = string.replace(dayRegex, '{{{04}}}');
string = string.replace(monthRegex, '{{{June}}}');
string = string.replace(yearRegex, '{{{2012}}}');

//string is now equal to "{{{Mon{{{04}}}ay}}} {{{04}}} {{{June}}} {{{2012}}}"

Answer 1

Update

Just realized this won’t work, but leaving it here for now until I can figure it out. It’s interesting nonetheless 🙂

Mimicking the lookbehind and lookforward assertions in regex:

var str = '{{{h}}}';
str.replace(/({{{)?h(}}})?/g, function($0, $1, $2) { 
    return $1 && $2 ? $0 : '{{{' +$0 + '}}}';
});

Returns:

{{{h}}}

See also: http://blog.stevenlevithan.com/archives/mimic-lookbehind-javascript

Update 2

Seeing how you’re using the expressions, I would use this construct instead:

string.replace(/[ndmy]/g, function($0) {
    switch ($0) {
        case 'n':
            return '{{{Monday}}}';

        case 'd':
            return '{{{04}}}';

        case 'm':
            return '{{{June}}}';

        case 'y':
            return '{{{2012}}}';
    }
})

Output:

{{{Monday}}} {{{04}}} {{{June}}} {{{2012}}}

This basically performs replacement without overlaps, so you don’t have to worry about previously braced expressions.