A review of basic JavaScript knowledge

1,javascript is a scripting language that is Object-and event-driven and has security performance;

Features of 2,javascript:

1) Add interactive events to HTML;

2) scripting language, similar to Java syntax;

3) Explanatory language, side execution side interpretation;

3, three ways to reference JavaScript in a Web page:

1) Add a script tag to the page;

2) referencing external JS files;

3) write directly in the HTML tag, <input type= "button" value= " onclick=" Javascript:alert ("welcome You"); />

4, Declaration and assignment of variables:

1) can be declared before the assignment;

2) Edge Declaration edge assignment;

3) do not declare direct assignment;

Recommendation: Variables are not declared error-prone, generally not recommended to use;

5, Data type:

Undefined,number (including integer and character), null,boolean,string (including single and double quotes),

6, String object:

1) Properties:

The string object. Length;

2) Method:

CharAt (index); : Returns the character specified as a position;

IndexOf (str, index);: Returns the position of the first occurrence of a specified string str in a string;

SUBSTRING (INDEX1,INDEX2): Returns a substring from index1 to Index2, and includes the corresponding character of the index index1, excluding index2 corresponding characters;

Split (): Splits a string into an array of strings;

7,typeof operator: Detects the return value type of a variable;

The return values are as follows:

Undefined,string,boolean,number,object (object in JavaScript, array, or null);

8, array:

To create an array:  var fruit=new Array (size); Size is the total number of elements

Assigning values to an array:

1) var fruit=new Array ("Apple", "orange", "peach", "banana");

2) var fruit=new Array (4);

fruit[0]= "Apple", fruit[1]= "Orange", fruit[2]= "peach"; fruit[3]= "banana";

Access array: array name [subscript];

9, common methods and properties of arrays:

Property: Length; Sets or returns the number of elements in the array;

Method:

Join (): Places all the elements in the array in a string and separates them with a delimiter, such as a landline number;

Sort (): sorts the array;

Push (): Adds one or more elements to the end of the array and returns the new length;

10,break: all loops after termination;

Continue: Terminates the current loop and continues the next cycle;　　

A review of basic JavaScript knowledge