JavaScript syntax

Type	Instance	Describe
Assignments, arithmetic, and bit operators	= + - * /	Described in the JS operator
Conditions, comparisons, and logical operators	== != < >	Described in the JS comparison operator

JavaScript statement

In HTML, javaScript statements issue commands to the browser. The browser knows what to do with the JavaScript statement.

Statements are separated by a sign:

x = 5 + 6;
y = x * 10;

JavaScript keywords

JavaScript statements usually begin with a keyword. Var keywords tell the browser to create a new variable:

var x = 5 + 6;
var y = x * 10;

JavaScript identifier

Like any other programming language, JavaScript retains some identifiers for its own use.

JavaScript also retains keywords that are not used in the current language version, but will be used in future JavaScript extensions.

The JavaScript identifier must start with a letter, underscore, or a dollar sign ($).

Subsequent characters can be letters, numbers, underscores, or dollar characters (numbers are not allowed as first characters so javaScript can easily separate identifiers and numbers).

Here are the most important reserved words in JavaScript(alphabetical):

abstract	else	instanceof	super
boolean	Enum	Int	switch
break	export	interface	synchronized
byte	extends	let	this
case	false	long	throw
Catch	final	native	throws
char	finally	new	transient
class	float	Null	true
const	for	package	try
continue	function	private	typeof
debugger	Goto	protected	Var
default	if	public	void
delete	implements	return	volatile
do	import	short	while
double	in	static	with

JavaScript comments

Not all JavaScript statements are "commands." The content after the // will be ignored by the browser:

I won't execute

JavaScript data type

JavaScript has several data types: numbers, strings, arrays, objects, and so on:

var length = 16; N umber is literally assigned by numbers
var points = x * 10; N umber is literally assigned by expression
var lastName = "Johnson"; S tring is literally assigned by string
var cars = ["Saab", "Volvo", "BMW"]; A rray is literally assigned by arrays
var person = {firstName:"John", lastName:"Doe"}; Object is literally assigned by an object

The concept of data types

Data types are a very important part of programming languages.

In order to manipulate variables, it is important to understand the concept of data types.

If you do not use data types, the following instances will not be executed:

16 + "Volvo"

16 Plus "Volvo" how is it calculated? Does this result in an error or output the following results?

"16Volvo"

You can try to execute the above code in your browser to see the effect.

You'll learn more about data types in the next chapters.

JavaScript function

JavaScript statements can be written within functions, which can be repeatedly referenced:

Refers to a function , which calls a function (executes a statement within a function).

function myFunction(a, b) {
return a * b; R eturns the result of a multiplied by b
}

JavaScript is case sensitive.

When writing JavaScript statements, be careful whether to turn off the case switch key.

The function getElementById is different from the getElementbyID.

Similarly, the variable myVariable is different from MyVariable.

Tip: In this site's programming practice, you can practice understanding the case sensitivity of JavaScript variables.

JavaScript character set

JavaScript uses Unicode character sets.

Unicode overrides all characters, including characters such as punctuation.

For further information, learn from our complete Unicode reference manual.

Did you know that?

	In JavaScript, it is common to name rules for hump methods, such as lastName (not lastname).

	JavaScript is the scripting language. T he browser executes the script code line by line as it reads the code. For traditional programming, all code is compiled before execution.

JavaScript syntax

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