Functions

Defining

function funct-name( ) {
    statements;
    return VALUE;
}
function funct-name( ARG, ARG ) {
    var VAR-NAME = VALUE;

    statements;
    return VALUE;
}
  • Define all functions in the <head>...</head> of an HTML page, to ensure that the function is not called before it's been defined.

Arguments

  • All arguments are passed by value.
  • If an object is passed and its properties are altered in the function, the changes will be visible outside of the function.
  • The arguments of a function are maintained in the special array "arguments" (zero-based).
arguments[0]               // The first argument
functionName.arguments[1]  // The second argument

arguments.length           // Number of arguments

Local variables

  • Local variables must be declared using the var keyword.
  • Any variable declared within a function without the var keyword is a global variable.

Examples

function multiply(x, y) {
    var product = x * y;
    return product;
}
var i = multiply(5, 7); 
function subtract(x, y) {
    return x - y;
}
var j = subtract(5, 3); 
function myConcat() {
    var result = "";   // Initialize the output.
    var separator = arguments[0];

    // For each argument (skipping the first one, which is the separator).
    for (var i = 1; i < arguments.length; i++) {
        if (i > 1) {
           result += separator;
        }
        result += arguments[i];
    }
    return result;
}

// Returns "red, orange, blue"
myConcat(", ", "red", "orange", "blue");