Convert arguments to object?

Question

I'm looking for a way to transform a list of function arguments to a single object, where each argument results in a property on the object with the appropriate name.

Basically, what I want to achieve is something such as:

const foo = function (a, b, c) {
  const args = getObjectFromArguments(a, b, c);
  // or: getObjectFromArguments(arguments);
  // or: getObjectFromArguments();

  console.log(args);
  // { a: 2, b: 3, c: 4 }
};

foo(2, 3, 4);

How can I do this without the need to provide the arguments' names as reference and as a string, ideally even without using more complex constructs? The call to getObjectFromArguments should be as simple as possible.

Any ideas?

You cannot do that, because variable names are not guaranteed to be available in run time. — zerkms
– zerkms, Commented Aug 3, 2016 at 7:24
How about getObjectFromArguments(arguments), grab the arguments which looks like an array but not actually an array. However you can loop them over. But names would be an issue because they could be anything. — Rohit416
– Rohit416, Commented Aug 3, 2016 at 7:26
@GoloRoden, can you please tell us your objective? Zoom out. Don't ask about this bit of code you've written. Ask us how to accomplish your actual goal. — Mulan
– Mulan, Commented Aug 3, 2016 at 7:27
My take on this is that a function is superfluous for this. The functionality you are looking for is part of the ES6 syntax. You just need to write { a, b, c } (with any arguments you want) instead of uselessFunction(a, b, c). — Quentin Roy
– Quentin Roy, Commented Aug 3, 2016 at 8:09

zerkms · Accepted Answer · 2016-08-03 07:25:29Z

2

It is not possible.

Not only the variable names are not generally available in run time, but they also might be changed (mangled) during minification (or any other transformation) process.

Also, the variable values are evaluated before values are passed as a function parameters. That makes existence of a general purpose function (like you named it getObjectFromArguments) even less possible.

From the other hand - the whole idea smells and might be a sign that you're doing something in a terribly weird way (but there might be exceptions from that indeed).

answered Aug 3, 2016 at 7:25

zerkms

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Comments

Community · Accepted Answer · 2017-05-23 12:14:47Z

1

A function is superfluous for this. The functionality you are looking for is already part of the ES6 syntax as a shorthand notation for object initialisation. You just need to write { a, b, c } instead of uselessFunction(a, b, c).

const foo = function (a, b, c) {
  const args = { a, b, c };
  console.log(args);
};

foo(2, 3, 4);

However, it is not possible using "only" the arguments object (your second example), and even less with a function that doesn't take any arguments (your last example). If you are looking for something like python's keyword arguments, it is not currently possible in JavaScript except by accepting only a single object as argument.

edited May 23, 2017 at 12:14

CommunityBot

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answered Aug 3, 2016 at 7:24

Quentin Roy

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8 Comments

zerkms Over a year ago

"How can I do this without the need to provide the arguments' names as reference"

Quentin Roy Over a year ago

@werkms I think it complies. The arguments' names are not provided as references. How I understand it, OP doesn't want to have an argument with an array of string containing the name of the properties of the resulting object.

zerkms Over a year ago

You provided them as a, b, c identifiers.

Quentin Roy Over a year ago

This is not an argument.

zerkms Over a year ago

The OP's aim is to have a general purpose function named getObjectFromArguments that can accept any number of arguments and that would infer the parameter names in runtime.

|

Quentin Roy · Accepted Answer · 2016-08-04 01:27:16Z

1

var foo = function(x,y,z) {
  console.log(getFnParamNames(arguments));
};

function getFnParamNames(args){
  var names =  args.callee.toString().match(/\(.*?\)/)[0].replace(/[()]/gi,'').replace(/\s/gi,'').split(','),
      result = {};
  for (var i in names) {
    result[names[i]] = args[i];
  }
  return result;
}

foo(2,3,4);

However, as this solution makes use of arguments.callee that is forbidden starting from ES5 in strict mode, it won't work in this case.

edited Aug 4, 2016 at 1:27

Quentin Roy

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answered Aug 3, 2016 at 8:01

pyda

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2 Comments

zerkms Over a year ago

It needs a note that it's not a standard JS (hence is not guaranteed to work).

pyda Over a year ago

Good point. You should read developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/…

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