Javascript Regex: reuse matches [duplicate]

Question

I have a function:

function process(str) {
    if (str == "Mary") {
        return "Sally";
    } else {
        return str;
    }
}

And I have some text:

John Smith
Mary Smith
Peter Smith
Mary Davis

I want it become:

John Smith
Sally Smith
Peter Smith
Sally Davis

But none of this work:

text = text.replace(/([a-zA-Z]+)\s([a-zA-Z]+)([\n]{0,1})/g,process(RegExp.$1) + " " + process(RegExp.$2)+"\$3");
//RegExp.$n is undefined

or

text = text.replace(/([a-zA-Z]+)\s([a-zA-Z]+)([\n]{0,1})/g,process('\$1') + " " + process('\$2')+"\$3");
//I got this exact string '$1' in process()

So how can I reuse the matches value and pass it into another function?

Use a function as the second parameter: String.prototype.replace — Andreas
– Andreas, Commented Oct 17, 2015 at 10:33

Ángela · Accepted Answer · 2015-10-17 10:51:39Z

1

String.prototype.replace can take a function as a second parameter. This function will have the match of the regex as the first parameter. So you only have to call replace like this:

var result = str.replace(/([a-zA-Z]+)/g, process);

Example: https://jsfiddle.net/71k6x3gd/

I also changed the regex to match all words, since surnames are never "Mary", it still works as expected. If you want to keep your regex, you would need to change the function to work with the parenthesized submatches. In the replacement function, these are the arguments following the match. Something like this:

function process(matchedString, firstName, secondName, optionalReturn) {
    if (firstName == "Mary") {
        firstName = "Sally";
    }
    return firstName + " " + secondName + optionalReturn;
};

Example: https://jsfiddle.net/71k6x3gd/1/

edited Oct 17, 2015 at 10:51

answered Oct 17, 2015 at 10:36

Ángela

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