Basics of getting started with JavaScript_javascript skills

Basic JavaScript syntax

1. Operator

An operator is a series of symbols that completes an operation. It has seven categories:

Assignment operators (=, =,-=,*=,/=,%=,<<=,>>=,|=,&=), arithmetic operators (,-,* ,/, ,--,%), comparison operators (>,<,<=,>=,==,===,!=,!==), logical operators (||, &&,!), conditional operation (?:), displacement operator (|,&,<<,>>,~,^) and string operator ( ). ​

Many people may not know what "===" is. ​

Here, let me explain to you that in JavaScript, "===" is congruent. Only the memory addresses on both sides of "===" are equal will return true.

And "==" will return true if the values ​​are equal.

For example: null==undefined will return true, but null===undefined will return false!

2. Expression

The combination of operators and operands is called an expression, which is usually divided into four categories: assignment expressions, arithmetic expressions, Boolean expressions and string expressions.

3. Statement

A Javascript program is composed of several statements, which are instructions for writing programs.

Javascript provides a complete set of basic programming statements, which are: assignment statement, switch selection statement, while loop statement, for loop statement, for each loop statement, do while loop statement, break loop interruption statement, continue loop interruption statement, with statement, try...catch statement, if statement (if..else, if...else if...), let statement.

4. Function

A function is a named statement segment that can be referenced and executed as a whole. Please pay attention to the following points when using functions:

1) Functions are defined by the keyword function (can also be constructed by the Function constructor);

2) Functions defined using the function keyword can be called anywhere within a scope (including before the statement that defines the function); while functions defined using the var keyword must be defined before they can be called;

3) The function name is the name quoted when calling the function. It is case-sensitive. You cannot write the wrong function name when calling the function;

4) Parameters represent the values ​​passed to the function for use or operation. It can be a constant, a variable, or a function. Inside the function, the arguments object can be passed (the arguments object is a pseudo array, and the attribute callee is referenced by function called) to access all parameters;

5) The return statement is used to return the value of the expression. ​

6) The yield statement throws an expression and interrupts function execution until the next call to next.

5. Object

An important function of Javascript is the object-oriented function. Through object-based programming, program development can be carried out in a more intuitive, modular and reusable way.

6. Events

Operations that occur when a user interacts with a web page are called events. Events can be triggered by users, page changes, or even events you can't see (such as Ajax interaction progress changes).

Most things are caused by user actions. For example, if the user presses the mouse button, a click event is generated. If the mouse pointer moves on the link, a mouseover event is generated, etc.

In Javascript, events are often used in conjunction with event handlers.

7. Variables

　such as var myVariable = "some value";

A variable has its type. In the above example, the type of myVariable is string (string)

Common types supported by JavaScript include:

object: object

array: array

number: number;

Boolean: Boolean value, with only two values: true and false, which takes up the least memory among all types;

null: a null value, the only value is null;

undefined: variables without definition or assignment

In fact, JavaScript variables are weak variable types. If you assign a string to it, it is a String. If it is a number, it is an integer.

is true or false, it is of boolean type (note that quotation marks are not allowed, otherwise it will be treated as a string).

The above content introduces the basic syntax of JavaScript for getting started with JavaScript. I hope it will be helpful to everyone.