JavaScript Tutorial
This page shows some of the functionality in JavaScript. Be sure to reference the official ECMAScript (JavaScript) manual when you can.
Comments
// this is a single line comment, which can appear at the end of any line
/*
this is a multi line comment,
which can appear anywhere
/
Functions
someFunction(); // this is a call to a function named someFunction, the code for that function will run when the function is called
someFunction(5, 400, 5000); // this is a call to a function, sending 3 parameters to it. a parameter is an input value for a function
// this is a function definition, which is a portion of code, don't forget the closing curly bracket to end the function definition
function someFunction() {
}
// this is a function definition, which takes 3 parameters. parameters are also called arguments
function someFunction(arg1, arg2, arg3) {
}
// this is a function without a name, also known as a lambda function
function() {};
// this is a function which adds 2 numbers
// the word return is used to set the output of the function, as well as to stop the function running at the expression after the word return
// the result of add(..) is stored inside a variable named result
function add(a, b) {
return a + b;
}
var result = add(40, 20);
Data Types
string
'this is a string'
"this is a string"
number
20
40.0
99e5
-20
-40.0
boolean
true
false
null
null
someVariable = null; // set a variable to null, the variable still exists
undefined
delete someVariable; // delete a variable, the variable no longer exists, and evaluates to undefined
object
{} // an empty literal object
{'aa':5, 'bb':10} // a object literal with 2 elements, element with key aa has value 5, and element with key bb has value 10
function SomeClass() {
}
var someObject = new SomeClass; // an object of class SomeClass
Data type symbol also exists.
Intrinsic Data Types
Array
[20, 50, 80] // an array with 3 elements, keys are 0 1 and 2, values are 20 50 and 80, respectively.
Function
function() {} // an empty function with no name
function someFuncName() // an empty function with a name
{
}
someFuncName = function() // an empty function with a name
{
}
Many other intrinsic data types exist, check section 6.1.7.4 of the JavaScript Manual.
Operators
Math Operators
+ - * / % // these are some mathematical operators
5 * 4 // results in 20
5 * 4 + 2 // results in 22
5 * (4 + 2) // results in 30
Variables
var someVariableName = 'some string value'; // this creates a local variable and assigns it a string value
someGlobalVariable = 50; // this either creates a global variable, or updates a variable, and assigns it a number value
Conditions
var someVariable = 500;
functipn print(text)
{
// code here
}
// if
if (someVariable < 1000) {
print('value is less than 1000');
}
// if and else
if (someVariable < 200)
print('value is less than 200');
else
print('value is 200 or more');
// if, else if and else
if (someVariable < 100)
print('value is less than 100');
else if (someVariable < 300)
print('value is less than 300');
else if (someVariable < 500)
print('value is less than 500');
else
print('value is 500 or more');
Loops
functipn print(text)
{
// code here
}
// integer loop
for (var i=0; i<20; i++) {
print(i);
}
// array loop
var someArray = [20,50,80];
for (var i in someArray) {
print(someArray[i]);
}