" JavaScript is a cross-platform, object-oriented scripting language. It is a small and lightweight language. Inside a host environment (for example, a web browser), JavaScript can be connected to the objects of its environment to provide programmatic control over them. "
This guide assumes you have the following basic background:
- ::marker " A general understanding of the Internet and the World Wide Web (WWW). "
" JavaScript and Java are similar in some ways but fundamentally different in some others. The JavaScript language resembles Java but does not have Java's static typing and strong type checking. JavaScript follows most Java expression syntax, naming conventions and basic control-flow constructs which was the reason why it was renamed from LiveScript to JavaScript. "
- 1
" To get started with writing JavaScript, open the Scratchpad and write your first "Hello world" JavaScript code: "
"function greetMe(yourName) { alert("Hello " + yourName); }
greetMe("World");
"
- 2
" You use variables as symbolic names for values in your application. The names of variables, called identifiers, conform to certain rules. "
" A JavaScript identifier must start with a letter, underscore (_), or dollar sign ($); subsequent characters can also be digits (0-9). Because JavaScript is case sensitive, letters include the characters "A" through "Z" (uppercase) and the characters "a" through "z" (lowercase). "
- 3
"
With the keyword var. For example, "
" This syntax
can be used to declare both local and global variables.
"
var x = 42.
" This syntax
can be used to declare both local and global variables.
"
- 4
"
By simply assigning it a value. For example, "
x = 42.
" This
always declares a global variable. It generates a strict JavaScript
warning. You shouldn't use this variant.
"
"
With the keyword let. For example,"
let y = 13.
" This syntax
can be used to declare a block scope local variable. See Variable scope
below.
"