How can I pre-set arguments in JavaScript function call? (Partial Function Application)

Question

I am trying to write a JavaScript function that will return its first argument(function) with all the rest of its arguments as preset parameters to that function.

So:

function out(a, b) {     document.write(a + " " + b); }  function setter(...) {...}  setter(out, "hello")("world"); setter(out, "hello", "world")(); 

Would output "hello world" twice. for some implementation of setter

I ran into an issue with manipulating the arguments array on my first try, but it seems there would be a better way to do this.

Answer 1

First of all, you need a partial - there is a difference between a partial and a curry - and here is all you need, without a framework:

function partial(func /*, 0..n args */) {   var args = Array.prototype.slice.call(arguments, 1);   return function() {     var allArguments = args.concat(Array.prototype.slice.call(arguments));     return func.apply(this, allArguments);   }; } 

Now, using your example, you can do exactly what you are after:

partial(out, "hello")("world"); partial(out, "hello", "world")();  // and here is my own extended example var sayHelloTo = partial(out, "Hello"); sayHelloTo("World"); sayHelloTo("Alex"); 

The partial() function could be used to implement, but is not currying. Here is a quote from a blog post on the difference:

Where partial application takes a function and from it builds a function which takes fewer arguments, currying builds functions which take multiple arguments by composition of functions which each take a single argument.

Hope that helps.