Skipping An Argument Using The Javascript .bind() Method

In JavaScript I can bind arguments to a function like so.. function foo(arg1, arg2) { console.log(arguments); } foo = foo.bind(this, 'bar'); When called, we get this output... foo

Solution 1:

No such functionality exists in JavaScript, but it would be fairly straightforward to implement a function that does the same thing:

functioncurryWithNulls(fn, thisObj) {
  var curriedArgs = Array.prototype.slice.call(arguments, 2);
  var length = curriedArgs.length;

  returnfunction() {
    var args = Array.prototype.slice.call(arguments);

    for (var i = 0; i < length || args.length; i++) {
      if (i >= length || curriedArgs[i] === null) {
        curriedArgs[i] = args.shift();
      }
    }
    return fn.apply(thisObj, curriedArgs);
  }
}

functionfoo(arg1, arg2, arg3, arg4) {
  console.log(arguments);
}

var curriedFoo = curryWithNulls(foo, this, 'bar', null, null, 'qux');
curriedFoo('baz', 'lel');
// => { '0': 'bar', '1': 'baz', '2': 'lel', '3': 'qux' }

This differs slightly from your example in that it requires a null for each skipped argument (whereas in your example you have a single null fill in for two arguments). This allows more complex constructions with curried arguments in any position, e.g.:

var curriedFoo2 = curryWithNulls(foo, this, null, 'bar', null, 'qux');
curriedFoo2('baz', 'lel');
// => { '0': 'baz', '1': 'bar', '2': 'lel', '3': 'qux' }

Solution 2:

No, you'd just be binding the null.

The function's parameters are the function's parameters; binding a null does exactly that, it doesn't redefine the function, it returns a new one with the same signature.

Solution 3:

It is possible with a functional composition:

var foo = function(arg1, arg2, arg3, arg4) { console.log(arguments); }
var bar = function(arg2, arg4) { 
    return foo.bind(this, 'bar', arg2, 'qux')();
}
bar('baz', 'lel');

or, with modern syntax:

constfoo = (arg1, arg2, arg3, arg4) => console.log(arguments);
constbar = (arg2, arg4) => foo.bind(this, 'bar', arg2, 'qux')();
bar('baz', 'lel');

or without bind at all:

constfoo = (arg1, arg2, arg3, arg4) => console.log(arguments);
constbar = (arg2, arg4) => foo(this, 'bar', arg2, 'qux', arg4);
bar('baz', 'lel');

P.S. Don't forget to call your binded function (note these () after bind);