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Inspect the names/values of arguments in the definition/execution of a JavaScript function

Answer 1

+3 A:

While I can't see any good reason for this,

var reg = /\(([\s\S]*?)\)/;
var params = reg.exec(func);
if (params) 
     var param_names = params[1].split(',');

assuming func is the name of your function

Jonathan Fingland 2009-05-27 10:28:19

Nice, thanks! I do have some good reasons for this :) ...and they are mostly related to wanting to replicate some working Python code that uses `inspect.getargspec()`, in JavaScript.

clemesha 2009-05-27 10:38:42

I'm still wondering though if this is the only way of doing such an inspection... there is no more elegant way?

clemesha 2009-05-28 20:45:00

nothing that I know of, no. It's certainly not a common way to do things in JavaScript.

Jonathan Fingland 2009-11-30 13:29:16

Note that it doesn't play well at all with minifiers that change variable names, so you should be really carefull when using this kind of hacks.

Grégoire Cachet 2009-12-17 22:16:10

@Grégoire: Honestly, it isn't a practice I'd advocate at all, but the OP question was fairly clear and this is the only way of getting those argument names. If a minifier is used, all you'll get is the new minified names, which, hopefully, should still be enough.

Jonathan Fingland 2009-12-18 00:15:27

Answer 2

A:

Sightly improved version of Jonathan Fingland's answer:

// Utility function to extract arg name-value pairs
function getArgs(args) {
    var argsObj = {};

    var argList = /\(([^)]*)/.exec(args.callee)[1];
    var argCnt = 0;
    var tokens;

    while (tokens = /\s*([^,]+)/g.exec(argList)) {
        argsObj[tokens[1]] = args[argCnt++];
    }

    return argsObj;
}

// Test subject
function add(number1, number2) {
    var args = getArgs(arguments);
    alert(args.toSource()); // ({number1:3,number2:4})
}

// Invoke test subject
add(3, 4);

Note: This only works on browsers that support arguments.callee.

(Also posted at http://stackoverflow.com/questions/1007981/how-to-get-function-parameter-names-values-dynamically-from-javascript/1009013#1009013)

Ates Goral 2009-06-17 19:18:46

This is not good because you have to run the function to get its arguments. The question was to get arguments from the definition.

Grégoire Cachet 2009-11-30 13:18:40

Answer 3

A:

Here's a version that uses higher order functions. The only thing I don't like about it is that you have to specify parameters as members of an array. But at least they only have to be specified once.

<!DOCTYPE html>

<html>
<head>
<meta charset="UTF-8">
<title></title>
<script type="text/javascript">
var withNamedParams = function(params, lambda) {
    return function() {
        var named = {};
        var max   = arguments.length;

        for (var i=0; i<max; i++) {
            named[params[i]] = arguments[i];
        }

        return lambda(named);
    };
};

var foo = withNamedParams(["a", "b", "c"], function(params) {
    for (var param in params) {
        alert(param + ": " + params[param]);
    }
});

foo(1, 2, 3);
</script>
</head>
<body>

</body>
</html>

Ionuț G. Stan 2009-06-18 09:14:27

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Inspect the names/values of arguments in the definition/execution of a JavaScript function

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