Declaring Functions

Functions, like variables, must be declared. Let’s declare a function double that accepts an argument called x and returns the double of x :

  1. function double(x) {
  2.     return 2 * x;
  3. }

Note: the function above may be referenced before it has been defined.

Functions are also values in JavaScript; they can be stored in variables (just like numbers, strings, etc …) and given to other functions as arguments :

  1. var double = function(x) {
  2.     return 2 * x;
  3. };

Note: the function above may not be referenced before it is defined, just like any other variable.

{% exercise %}
Declare a function named triple that takes an argument and returns its triple.
{% solution %}
var triple = function(x) {
return x * 3;
}
{% validation %}
assert(triple);
assert(triple(4) === 12);
assert(triple(10) === 30);
{% endexercise %}