Python DAY14 JavaScript

OneECMAScript

Although ECMAScript is an important standard, it is not the only part of JavaScript, and certainly not the only one that is standardized. In fact, a complete JavaScript implementation is made up of the following 3 different parts:

• Core (ECMAScript)
• Document Object Model (DOM) Documents object models (consolidated js,css,html)
• Browser object models (BOM) Broswer object Model (integrated JS and browser)
• The vast majority of Javascript in development is object-based. It is also object-oriented.

To put it simply, ECMAScript describes the following:

• Grammar
• Type
• Statement
• Key words
• Reserved words
• Operator
• Object (encapsulates inherited polymorphism) object-based language. Use an object.

Ii. Basics of JavaScript 1. Access mode

1.html head with script tag    <script>        alert (' Hello Yuan ')    </script>2 import file    <script src= " Hello.js "></script>

2.js Variable Constants

(1). Declare a variable without declaring the variable type. All use the var keyword;

var A;

　　

(2). a row can declare multiple variables. And can be of different types

var name= "Yuan", age=20, job= "lecturer";

(3). you can declare variables without var. if you don't use Var then it's a global variable

(4). variable name, the first character can only be letter, underscore, $ dollar symbol three select one, the remaining characters can be underscores, dollar signs or any alphanumeric characters and case-sensitive, x and X is two variables

3. Constants and identifiers

(1). Consists of letters, numbers, underscores (_), Dollar signs ($) that do not begin with a number

(2). Names commonly used to denote functions, variables, etc.

(3). For example: _ABC, $ABC, abc,abc123 is an identifier, and 1ABC is not

(4). Words that represent a particular meaning in the JavaScript language are called reserved words and do not allow programs to be redefined as identifiers

4.js Data types

　

Python DAY14 JavaScript