JavaScript: Successively calling a list of functions on an object

Question

Let's say I have a list of functions stored in an array:

var myFunctions = [
    function (i) {return i + 2},
    function (i) {return i * 2},
    function (i) {return i - 3}
]

What would be the best way to successively call all these functions an object, i.e. to get ((n + 2) * 2) - 3 as a result?

Answers using external libraries like Underscore are welcome :)

Answer 1

Arrays are also JavaScript objects. In your case, you created an array and three properties to it, namely f1, f2 and f3. Instead, you can simply do

var myFunctions = [
    function(i) {
        return i + 2
    },
    function(i) {
        return i * 2
    },
    function(i) {
        return i - 3
    }
];

Now that we have an array of functions, we can use Array.prototype.reduce function to apply these functions like this

var result = myFunctions.reduce(function(result, currentFunction) {
    return currentFunction(result);
}, n);

The n is the actual initial value to be passed to the list of functions to be applied. reduce takes the initial value and the first function and passes them as the result and currentFunction respectively. We apply the currentFunction on result and return the value. In the next iteration, the returned value will be the result and the currentFunction will be the second function and so on.

If you don't like the functional approach, you can simply use a for loop, like this

var i = 0, result = 0, n = 10;
for (var i = 0; i < myFunctions.length; i += 1) {
    n = myFunctions[i](n);
}