JavaScript is a programming language. Syntax Rules define the language structure.
JavaScript syntax
JavaScript is a programming language. Syntax Rules define the language structure.
JavaScript syntax
JavaScript is a scripting language.
It is a lightweight but powerful programming language.
JavaScript literal
In programming languages, a literal is a constant, such as 3.14.
Number can be an integer, a decimal Number, or a scientific count (e ).
3.141001123e5
Strings can be enclosed in single quotes or double quotes:
"John Doe"'John Doe'
The expression literal is used for calculation:
5 + 65 * 10
An Array (Array) literally defines an Array:
[40, 100, 1, 5, 25, 10]
The Object literally defines an Object:
{firstName:"John", lastName:"Doe", age:50, eyeColor:"blue"}
The Function literally defines 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 uses equal signs to assign values to variables:
var x, lengthx = 5length = 6
Variables can be accessed by the variable name. In a script language, variables are usually variable. A literal is a constant value.
A variable is a name. A literal is a value.
JavaScript Operators
JavaScript uses arithmetic operators to calculate values:
(5 + 6) * 10
JavaScript uses the assign operator to assign values to variables:
x = 5y = 6z = (x + y) * 10
JavaScript has multiple types of operators:/p>
Type
Instance
Description
Value assignment, arithmetic and bitwise operators = +-*/description in JS Operators
Condition, comparison and logical operator =! = <> Description in JS comparison Operators
JavaScript statements
In HTML, the JavaScript statement sends a command to the browser.
The statement is separated by semicolons:
x = 5 + 6;y = x * 10;
JavaScript keywords
JavaScript statements generally start with a keyword. Var keyword tells 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 some 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 dollar sign ($.
Subsequent characters can be letters, numbers, underscores, or dollar signs (numbers are not allowed to appear as the first character, so that JavaScript can easily distinguish between identifiers and numbers ).
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
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 Type
JavaScript has multiple data types: Numbers, strings, arrays, objects, and so on:
Var length = 16; // Number value through the Number literal var points = x * 10; // Number value through the expression literal var lastName = "Johnson "; // String value: var cars = ["Saab", "Volvo", "BMW"]; // Array value: var person = {firstName: "John", lastName: "Doe"}; // assign a value through the Object literal
Concept of Data Types
In programming languages, data types are very important.
To operate variables, it is very important to understand the concept of data types.
If the data type is not used, the following instances cannot be executed:
16 + "Volvo"
16 plus "Volvo", how is computing? Will the above generate an error or output the following results?
"16Volvo"
You can view the effect by executing the above Code in the browser.
In the following sections, you will learn