Javascript regex - getting function name from string

Question

I am trying to get a function name from a string in javascript.

Let's say I have this string:

function multiply($number) {
    return ($number * 2);
}

I am using the following regex in javascript:

/([a-zA-Z_{1}][a-zA-Z0-9_]+)\(/g

However, what is selected is multiply(. This is wrong. What I want is the word multiply without the the (, though the regex should keep in mind that the function name must be attached an (.

I can't get this done. How can I make the proper regex for this? I know that this is not something I really should do and that it is quite error sensitive, but I still wanna try to make this work.

Just don't get the whole match but only the capturing group. — Bergi, Dec 05 '17 at 22:26
You'll want to notice that there are many function in javascript that this regex will not match, or in the wrong position. — Bergi, Dec 05 '17 at 22:27
On the night of a full moon, just past midnight, you might try `eval(\`(${string})\`).name` — le_m, Dec 05 '17 at 23:34
I added the `{1}`, to make sure the first character starts with a valid character, but since the second character class is the same, it is not needed. — DijkeMark, Dec 06 '17 at 17:07

score 4 · Accepted Answer · answered Dec 05 '17 at 22:26

4

Just replace last \) with (?=\()

`function multiply($number) {
    return ($number * 2);
}`.match(/([a-zA-Z_{1}][a-zA-Z0-9_]+)(?=\()/g) // ["multiply"]

answered Dec 05 '17 at 22:26

gurvinder372

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This was the simplest solution that worked for me, thanks! – DijkeMark Dec 06 '17 at 17:15

ibrahim mahrir · Answer 2 · 2017-12-05T22:39:08.913

You can use:

var name = functionString.match(/function(.*?)\(/)[1].trim();

Get anything between function and the first ( (using a non-gredy quantifier *?), then get the value of the group [1]. And finally, trim to remove surrounding spaces.

Example:

var functionString = "function dollar$$$AreAllowedToo () {  }";

var name = functionString.match(/function(.*?)\(/)[1].trim();

console.log(name);

Notes:

The characters allowed in javascript for variable names are way too much to express in a set. My answer takes care of that. More about this here
You may want to consider the posibility of a comment between function and (, or a new line too. But this really depends on how you intend to use this regex.

take for examlpe:

function /*this is a tricky comment*/ functionName // another one
   (param1, param2) {

}

Though it seems to work, the other answer suits my needs slightly better. Thanks. — DijkeMark, Dec 06 '17 at 17:16

Javascript regex - getting function name from string

2 Answers2