Javascript explode object to arguments

Question

Is there some way to make the following work in javascript?

var orders = [
   {milk: true, sugar: "extra"}, 
   {milk: false, sugar: "normal"}
   ];

function makeCoffee(sugar, milk) {
    console.log(sugar);
    console.log(milk);
}

orders.forEach(makeCoffee);

They easiest way would to make `makeCoffee` accept a single object with the arguments. Since object properties are unordered the only way to pass the properties in the right order is to parse the function signature and extract the parameter names. I don't think that's worth it. — Felix Kling, Jul 31 '12 at 09:16
But it really is more flexible and relatively common to do so, why are you trying to avoid it? — Felix Kling, Jul 31 '12 at 09:17
@FelixKling it works, but it litters the code i.e. `function makeCoffee(dummy) {console.log(dummy.milk); console.log(dummy.sugar);}`. Anyways, the question is about if or not something like this is possible - debate about their pros and cons is for another day :) — Manav, Jul 31 '12 at 09:19

Felix Kling · Accepted Answer · 2012-07-31T09:35:50.540

As I said in my comment, in browsers where func.toString() returns the source of the function ^†, you could parse the signature and extract the parameter names:

var arg_names = makeCoffee.toString()
            .match(/function[^(]*\(([^)]*)\)/)[1].split(', ');

orders.each(function(order) {
    makeCoffee.apply(null, arg_names.map(function(name) {
        return order[name];
    });
});

Since JavaScript does not provide any reflection API, this is probably the only way.

If you don't explicitly state in which browsers your code is supported, this might not work (I don't know what IE returns for func.toString). I still recommend to pass an object as argument.

†: The exact representation of the function is implementation dependent though. Here is the corresponding description from the specification:

An implementation-dependent representation of the function is returned. This representation has the syntax of a FunctionDeclaration. Note in particular that the use and placement of white space, line terminators, and semicolons within the representation String is implementation-dependent.

Brilliant! and unusable :) - I'll accept this (if nothing better comes along) because it shows that something of this sort can be done, not because it should be done. — Manav, Jul 31 '12 at 09:43

score 0 · Answer 2 · answered Jul 31 '12 at 09:13

0

The best I can come up with till now is:

function makeCoffee() {
    console.log(this.milk);
    console.log(this.sugar);
}

orders.forEach(function(x) {makeCoffee.call(x)})

Pros:

Works

Cons (IMO):

it introduces unnecessary coupling between the order and makeCoffee (sort of like how the composition vs inheritance thing panned out).
we lose the explicitness of the makeCoffee function declaring its inputs

answered Jul 31 '12 at 09:13

Manav

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Answering your own questions bad habit, You could have added this code in your question my friend. – yogi Jul 31 '12 at 09:16

Eugen Rieck · Answer 3 · 2012-07-31T09:39:13.410

0

I recommend this:

//Should go to config.js
var COFFEE_SUGAR_DEFAULT="normal";

var orders = [
   {milk: true, sugar: "extra"}, 
   {milk: false, sugar: "normal"}
   ];

function makeCoffee(coffeeDefinition) {
    if (!coffeeDefinition.sugar) coffeeDefinition.sugar=COFFEE_SUGAR_DEFAULT;
    if (!coffeeDefinition.milk) coffeeDefinition.milk=false; //might not be a real boolean
    console.log(coffeeDefinition.sugar);
    console.log(coffeeDefinition.milk);
}

orders.forEach(function(x) {makeCoffee(x)})

pros:

works and is robust
introduces just the necessary coupling
is expandable to e.g. "decaffeinated":false

cons:

not pretty

edited Jul 31 '12 at 09:39

answered Jul 31 '12 at 09:24

Eugen Rieck

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I am sorry if I miscommunicated. This is not what I wanted to ask (I really shouldn't have answered my own question - it is perhaps taking the discussion on a tangent). Your solution is about making the implicit binding that was achieved through using the `this` object explicit by using a `coffeeDefinition` (which is a worthy goal). My actual question is if or not some sort of "automatic exploding" is possible. – Manav Jul 31 '12 at 09:30
It is not, and it should not. A n item in `orders` and the `mekaCoffee()` function **are** linked - one is useless without the other – Eugen Rieck Jul 31 '12 at 09:39

Javascript explode object to arguments

3 Answers3