Question

I was gearing up for Javascript, reading the tutorials at W3Schools and came across this code:

function sortNumber(a, b)
{
return a - b;
}

var n = ["10", "5", "40", "25", "100", "1"];
document.write(n.sort(sortNumber));

It sorts the elements in the Array, pretty simple. But how can we pass sortNumber ( a function name) as a parameter to the sort function?

The original example

Answer 1

Surprisingly, JavaScript has its roots in a language called Scheme.

Scheme allows certain functions (called ‘lambda functions’) to be passed around as though they were a variable.

JavaScript handles functions in much the same way scheme did. (Some people say that “functions are first-class-citizens in JavaScript.”)

For example, you can write:

// Assign a function to foo
var foo = function () { alert('bar'); };

// Call foo like a function
foo();

The result would be that the message ‘bar’ is shown.

The classic example of lambdas is the “Adder” example:

adder = function (x) {
    return function (y) {
        x + y
    }
};
add5 = adder(5);
add5(1); // == 6

Hope this helps.