Question

When should I use something like this versus a regular Switch statement? What are the pros and cons of each?

function ABC(i, j, a) {
  var ops = {
    'add': function(i, j) { return i + j; },
    'minus': function(i, j) { return i - j; },
    'multiply': function(i, j) { return i * j; },
    'random': function(i, j) {
      return ops[['add', 'minus', 'multiply'][Math.floor(Math.random() * 3)]](i, j);
    }
  };
  return ops[a](i, j);
}

Answer 1

Pros:
It is much more flexible. You can define the functions anywhere, and you can reassign them at runtime, or even generate the dictionary programatically, which is a big win if there are patterns that you can factor out. You can also reuse the dictionary later, or pass it around.

Cons:
In a compiled language, it’s likely slower. (With a JIT it shouldn’t really matter.)
For small code snippets, the switch version is more readable.

Personally I’d prefer the dict approach, but then again I code primarily in Python.