1.1 Core JavaScript
This section is a tour of the JavaScript language.
Types, Values, and Variables
| // variable is a symbolic name for a value.
// Variables are declared with the var keyword:
var x; // Declare a variable named x.
// Values can be assigned to variables with an = sign
x = 0; // Now the variable x has the value 0
x // => 0: A variable evaluates to its value.
// JavaScript supports several types of values
x = 1; // Numbers.
x = 0.01; // Just one Number type for integers and reals.
x = "hello world"; // Strings of text in quotation marks.
x = 'JavaScript'; // Single quote marks also delimit strings.
x = true; // Boolean values.
x = false; // The other Boolean value. x = null; // Null is a special value that means "no value".
x = undefined; // Undefined is like null.
|
Two other very important types that JavaScript programs can manipulate are
objects and arrays
| // JavaScript's most important data type is the object.
// An object is a collection of name/value pairs, or a string to value map.
var book = { // Objects are enclosed in curly braces.
topic: "JavaScript", // The property "topic" has value "JavaScript".
fat: true // The property "fat" has value true.
}; // The curly brace marks the end of the object.
// Access the properties of an object with . or []:
book.topic // => "JavaScript"
book["fat"] // => true: another way to access property values.
book.author = "Flanagan"; // Create new properties by assignment.
book.contents = {}; // {} is an empty object with no properties.
// JavaScript also supports arrays (numerically indexed lists) of values:
var primes = [2, 3, 5, 7]; // An array of 4 values, delimited with [ and ].
primes[0] // => 2: the first element (index 0) of the array.
primes.length // => 4: how many elements in the array.
primes[primes.length-1] // => 7: the last element of the array.
primes[4] = 9; // Add a new element by assignment.
primes[4] = 11; // Or alter an existing element by assignment.
var empty = []; // [] is an empty array with no elements.
empty.length // => 0
// Arrays and objects can hold other arrays and objects:
var points = [ // An array with 2 elements.
{x:0, y:0}, // Each element is an object.
{x:1, y:1}
];
var data = { // An object with 2 properties
trial1: [[1,2], [3,4]], // The value of each property is an array.
trial2: [[2,3], [4,5]] // The elements of the arrays are arrays.
};
|
2.1 Character Set
2.1.1 Case Sensitivity
E.x. online, Online, OnLine, and ONLINE are four distinct variable names.
2.3 Literals
{ x:1, y:2 } // An object initializer
[1,2,3,4,5] // An array initializer
2.4 Identifiers and Reserved Words
In JavaScript, identifiers are used to name variables andfunctions and to provide labels for certain loops in JavaScript code. A JavaScript identifier must begin with a letter, an underscore (_), or a dollar sign ($).
These are all legal identifiers:
i
my_variable_name
v13
_dummy
$str