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In this article, the editor introduces "what is the core grammar of JavaScript" in detail, the content is detailed, the steps are clear, and the details are handled properly. I hope this article "what is the core grammar of JavaScript" can help you solve your doubts.

What is JavaScript?

JavaScript is an object-based and event-driven scripting language with security performance, which has been widely used in Web application development. It is often used to add a variety of dynamic functions to web pages and provide users with a more smooth and beautiful browsing effect. Usually JavaScript scripts implement their own functions by embedding them in HTML.

Characteristics of JavaScript

JavaScript composition

Daily use of JavaScript

The basic structure of JavaScript

Example:

... Can be included anywhere in the document, as long as the code is read and loaded into memory before being used

The implementation principle of JavaScript

The way JavaScript is referenced in a web page

1. Use label

two。 External JS file

3. Directly in the HTML tag

JavaScript core syntax:

① declares variables before assigning values

Var width

Width=5

Var-keyword used to declare variables

Width-variable name

② declares and assigns variables simultaneously

Var catName= Pippi

Var x, y, zonal 10

③ does not declare direct assignment [generally not used]

Width=5

Variables can be used directly without declaration, but this method is error-prone, difficult to find and debug, and is not recommended.

① undefined: example: var width

The variable width has no initial value and will be assigned the value undefined

② null: represents a null value equal to the undefined value

③ number:

Var iNum=23; / / Integer

Var iNum=23.0;? / / floating point number

④ Boolean:true and false, but JS will parse them into 1 position 0.

⑤ String: a group of text var string1= "This is a string" enclosed in quotation marks (single or double quotation marks)

The return value of typeof detection variable; the return value of typeof operator is as follows:

① undefined: the variable is declared but not assigned.

② string: a string declared in single or double quotation marks.

③ boolean:true or false.

④ number: integer or floating point number.

Objects, arrays, and null in ⑤ object:javascript.

① attribute:

String object. Length

Var str= "this is JavaScript"

Var strLength=str.length;? / / length is 18

② method:

String object. Method name ()

Split (str): if the syntax is written as width.split ("") [space between colons] then: width height hello world will be split into: width,height,hello,world If the grammar is written as width.split (") [there is no space between colons] at this point: width height hello world will be split into: wrecery iMagiRegy t, hPerry ePersonnce gPercience hPerry, hPerry ePersonlPersonlPersonlPerspectiveo, wPhonePersonlMagnedPersonlMagol d.

① creates an array:

② assigns values to array elements:

Method 1: var fruit=new Array ("apple", "orange", "peach", "banana")

Method 2:

Var fruit=new Array (4)

Fruit [0] = "apple"

Fruit [1] = "orange"

Fruit [2] = "peach"

Fruit [3] = "banana"

③ access array:

Array name [subscript]

More methods can be found in the JavaScrpt Array object reference manual:

① if conditional statement

Zero zero null, "", undefined,NaN,false- in If turns out to be false; and everything else is true!

② switch multi-branch statement

③ for, while Loop statement

④ for-in

I is the subscript of the array. In this array needs to query all array subscripts.

① break

② continue

The ① one-line comment begins with / / and ends with the end of the line:

/ / alert ("Congratulations! successful registration")

/ / A prompt for the success of a registered member pops up on the same page as above

/ / comment

If you enter and type something in a single-line comment on the page, you will get an error: Uncaught ReferenceError: XXXX is not defined

The ② multiline comment ends with a symbol indicating that the middle statement is a comment in the program

[output generally uses alert; input using prompt;, but later use of alert is not recommended, and console.Log () is generally used in real development]

① alert () [commonly used in warnings or prompts]:

Alert ("prompt message")

② prompt ()

Prompt ("prompt message", "default information for input box")

Prompt ("Please enter your favorite color", "red")

Prompt ("Please enter your favorite color", ")

① code is case sensitive

An error will be reported when lowercase is uppercase: Uncaught SyntaxError: Unexpected identifier

Names of ② variables, objects, and functions

When declaring the names of variables, objects, and functions, uppercase, number, underscore, dollar sign are fine, but they must start with letters, underscores, and dollar signs.

Otherwise, an error will be reported: Uncaught SyntaxError: Invalid or unexpected token

③ semicolon

If you don't write it, you will get an error: Uncaught SyntaxError: Invalid or unexpected token

Print the information directly and see the specific information directly on the page

[but generally use console.Log (), because using alert () is easy to forget to delete, when using alert () for pop-up, the final product launch will reduce the user experience, so using console.Log () will avoid this problem]

Meaning of function: similar to the method in Java, it is a block of code statements that accomplish a specific task; it is easier to use: do not have to define belonging to a class, but use it directly; function classification: system functions and custom functions

ParseInt ("string"): converts a string to an integer number

For example, parseInt ("86") converts the string "86" to an integer value of 86

When parseInt ("86a"), the output is still 86

The output is still 86 when parseInt ("86a21")

Output NaN when parseInt ("a86a")

ParseFloat ("string"): converts a string to a floating point number

For example, parseFloat ("34.45") converts the string "34.45" into a floating point value of 34.45

IsNaN (): used to check whether its parameter is non-numeric

IsNaN ("111") outputs false

IsNaN (true) outputs false

IsNaN ("true") outputs true

IsNaN ("aaa") outputs true

IsNaN ("111a") outputs true

Custom function

1. Define function

two。 Call function

Function calls are generally used with events of form elements, calling format

Event name =? "function name ()"?

First, call no-parameter function

Call the no-parameter function and output "Welcome to learn JavaScript" 5 times.

Example:

When you click this button, call the function study (? ) to execute the code in the function body

Second, call the function with parameters

According to the number of times you enter, "Welcome to learn JavaScript" is displayed.

Example:

When you click this button, call the function study (count) to execute the code in the function body

After reading this, the article "what is the Core Grammar of JavaScript" has been introduced. If you want to master the knowledge points of this article, you still need to practice and use it yourself to understand it. If you want to know more about related articles, welcome to follow the industry information channel.

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