Replacement Text Syntax for JavaScript’s String.replace()
A RegexBuddy user told me that he couldn’t easily find a detailed explanation of the replacement text syntax supported by the String.replace() function in JavaScript. I had to admin that my own web page about JavaScript’s regular expression support was also lacking. I’ve now added a new Replacement Syntax section that has all the details. I’ll summarize it here:
$1: Text matched by the first capturing group or the literal text $1 if the regex has no capturing groups.$99: Text matched by the 99th capturing group if the regex has 99 or more groups. Text matched by the 9th capturing group followed by a literal 9 if the regex has 9 or more but less than 99 groups. The literal text $99 if the regex has fewer than 9 groups.$+: Text matched by the highest-numbered capturing group. Replaced with nothing if the highest-numbered group didn’t participate in the match.$&: Text matched by the entire regex. You cannot use$0for this.$`(backtick): Text to the left of the regex match.$'(single quote): Text to the right of the regex match.$_: The entire subject string.
This list is missing $$, which inserts a single dollar sign.
Also note that $+ and $_ are not part of the JavaScript specification and should not be used. Anywhere they are supported, they are browser-specific extensions. Specifically, $_ works in IE only, and $+ works in IE and Firefox only. Neither work in the current versions of Chrome, Safari, or Opera.
Comment by Steven Levithan — Thursday, 10 June 2010 @ 18:23
I’ve updated the JavaScript and flavor comparison pages to clarify that these are browser-specific extensions. (Which I should have known because we got it right in chapter 2 of our book.)
Comment by Jan Goyvaerts — Friday, 11 June 2010 @ 16:25