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 %}