JavaScript Syntax
JavaScript is a programming language. The grammar rules define the structure of the language.
JavaScript Syntax
JavaScript is a scripting language.
It is a lightweight but powerful programming language.
JavaScript Literal
In programming languages, generally fixed values are called literals, such as 3.14.
Number (Number) literal can be an integer or decimal, or scientific notation (e).
3.14
1001
123e5
String literals can use single or double quotes:
"John Doe"
'John Doe'
Expression literals are used in calculations:
5 + 6
5 * 10
Array literal Define an array:
[40, 100, 1, 5, 25, 10]
Object literal defines an object:
{firstName:"John", lastName:"Doe", age:50, eyeColor:"blue"}
Function literal Define a function:
function myFunction(a, b) {return a * b;}
JavaScript Variables
In programming languages, variables are used to store data values.
JavaScript uses the keyword var to define variables and the equal sign to assign values to variables:
var x, length x = 5 length = 6
Variables can be accessed by variable name. In imperative languages, variables are usually mutable. The literal is a constant value.
 | The variable is a name . The literal is a value . |
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JavaScript Operators
JavaScript uses arithmetic operators calculated value:
(5 + 6) * 10
JavaScript uses assignment operators to assign values to variables:
x = 5 y = 6 z = (x + y) * 10
There are many types of operators in the JavaScript language:
| Type | Example | Description |
|---|---|---|
| Assignment, arithmetic and bit operators | = + - * / | Described in JS operators |
| Conditions, comparisons and logical operators | == != <> | Described in JS comparison operators |
JavaScript Statement
In HTML, a command issued by a JavaScript statement to the browser.
The statements are separated by semicolons:
x = 5 + 6;
y = x * 10;
JavaScript Keywords
JavaScript keywords are used to identify the action to be performed.
Like any other programming language, JavaScript reserves some keywords for its own use.
The var keyword tells the browser to create a new variable:
var x = 5 + 6; var y = x * 10;
JavaScript also retains some keywords, which are not used in the current language version, but will be used in future JavaScript extensions.
The following are the most important reserved words in JavaScript (in alphabetical order):
| 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 double slash // will be ignored by the browser:
// I will not execute
JavaScript Data Types
JavaScript has many data types: numbers, strings, arrays, objects, etc.:
var length = 16; // Number is assigned by number literal
var points = x * 10; // Number is assigned by expression literal
var lastName = "Johnson"; // String is assigned by string literal
var cars = [" Saab", "Volvo", "BMW"]; // Array is assigned by array literal
var person = {firstName:"John", lastName:"Doe"}; // Object is assigned by object literal
The Concept of Data Types
In programming languages, data types are a very important content.
In order to be able to manipulate variables, it is important to understand the concept of data types.
If the data type is not used, the following examples will not be executed:
16 + "Volvo"
16 How to add "Volvo" to calculate? Will the above produce an error or output the following result?
"16Volvo"
You can try to execute the above code in your browser to see the effect.
In the following chapters you will learn more about data types.
JavaScript Function
JavaScript statements can be written in functions, and functions can be quoted repeatedly:
Reference a function = call function (execute the statement within the function).
function myFunction(a, b) {
return a * b; // return the result of a multiplied by b
}
JavaScript Letter Case
JavaScript is case sensitive.
When writing JavaScript statements, please pay attention to whether to turn off the case switch key.
The function getElementById is different from getElementbyID .
Similarly, the variables myVariable and MyVariable are also different.
JavaScript Character Set
JavaScript uses the Unicode character set.
Unicode covers all characters, including characters such as punctuation.
For more information, please study our full Unicode reference manual.
Do you know?
| In JavaScript, the common camel case naming rule, such as lastName (not lastname). |
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