javascript

Chapter 5: Reference Types
Sequence
Replacement Text
$$ $
$ & The substring matching the entire pattern. Same as RegExp.lastMatch .
$’ The part of the string occurring before the matched substring. Same as RegExp
.leftContext.
$` The part of the string occurring after the matched substring. Same as RegExp
.rightContext.
$n The n th capture, where n is a value 0 – 9. For instance, $1 is the first capture, $2 is
the second, etc. If there is no capture then the empty string is used.
$nn
The nn th capture, where nn is a value 01 – 99. For instance, $01 is the first capture,
$02 is the second, etc. If there is no capture then the empty string is used.
Using these special sequences allows replacement using information about the last match, such as in this
example:
var text = “cat, bat, sat, fat”;
result = text.replace(/(.at)/g, “word ($1)”);
alert(result); //word (cat), word (bat), word (sat), word (fat)
Here, each word ending with “ at ” is replaced with “ word ” followed in parentheses by what it replaces
by using the $1 sequence.
The second argument of replace() may also be a function. When there is a single match, the function
gets passed three arguments: the string match, the position of the match within the string, and the whole
string. When there are multiple capturing groups, each matched string is passed in as an argument, with
the last two arguments being the position of the pattern match in the string and the original string. The
function should return a string indicating what the match should be replaced with. Using a function as
the second argument allows more granular control over replacement text, as in this example:
function htmlEscape(text){
return text.replace(/[ < > ” & ]/g, function(match, pos, originalText){
switch(match){
case “ < ”:
return “ & lt;”;
case “ > ”:
return “ & gt;”;
case “ & ”:
return “ & amp;”;
case “\””:
return “ & quot;”;
}
});
}
alert(htmlEscape(“ < p class=\”greeting\” > Hello world! < /p > ”));
//” & lt;p class= & quot;greeting & quot; & gt;Hello world! & lt;/p & gt”;
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