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);

Answer 1

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.

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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.

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†: 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.