JavaScript Basics -1 JavaScript (overview, basic syntax)

First, JavaScript overview

JavaScript Concepts

-JavaScript is an interpreted scripting language that runs in JavaScript interpreter/engine

-JavaScript interpreter as the operating environment of JS script, like the next two rendering methods

-Standalone JavaScript interpreter for installation;

-JavaScript interpreter embedded in the browser kernel;

-The main browsers installed in PCs, tablets, mobile phones, and set-top boxes all support JavaScript

JavaScript history

-In 1992, Nombas developed a scripting language scriptease for its own Cenvi software, which can be embedded in Web pages

-in 1995, Netscape company developed another client-side scripting language livescript for its own Navigator2.0 browser, renamed JavaScript for the fashion, but it has nothing to do with Java.

-in 1996, in order to enter the browser market, Microsoft launched a JavaScript clone version in IE3.0 browser called JScript

-in 1997, JavaScript 1.1 was presented to ECMA as a draft, with various manufacturers pulling out of the ECMA-262 standard, defining a new ECMAScript standard scripting language, and major browser manufacturers starting to "work" to ECMAScript as the standard and target for implementation

-The full JavaScript language consists of three parts:

-Core (ECMAScript)

-Document Object Model (dom,document)

-Browser object Model (Bom,browser)

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JavaScript Features

-code can be written using any text editing tool, syntax similar to C and Java

-No need to compile, interpreted by JavaScript engine execution

-Weakly typed language

-Based on object

-Use

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Second, JavaScript basic syntax

Browser kernel

-the browser core is responsible for rendering the content of the page, consisting mainly of two parts:

-Content Typesetting engine-----parsing HTML/CSS

-Script Interpretation engine-----parsing JavaScript

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Build JavaScript Runtime Environment

-Install a standalone JavaScript interpreter

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-Use the JavaScript interpreter embedded in the browser kernel

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The first JavaScript program

-Way One: Use the standalone JavaScript interpreter

-You can enter the script to execute in one line and execute

-You can also write multiple lines of script to execute in a text file, batch execution

-Way Two: Use the embedded JavaScript interpreter in the browser kernel

-Enter the script directly in the console and execute

-Embed the JS script in the HTML page to execute

-HTML element events

-<script> Elements

-External script file

HTML element Events

-Script statements to be executed are written directly in the <body> tab

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<script> elements

-Multiple statements can be executed in an internal script block

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External script files

-Write JavaScript code to a separate file and save it as a file with the suffix. js

-For plain text files

-No need to include <script> tags in the file, write JS code directly

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-Reference the. js file in the HEAD of the HTML page

-Add <script> tags to

-Set the "src" attribute of the <script> tag to develop the URL of the JS file

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Third, JavaScript debugging

JavaScript Code Error

-interpreted language, if a line of code is wrong, the interpreter terminates this line

-but does not affect subsequent block execution, and subsequent parsing of HTML elements

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debugging features of the browser

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Chrome Control Console

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Iv. JavaScript Syntax specification

Writing JavaScript Code

-statement----will be interpreted by the JavaScript engine to execute the code

-consists of an expression, a keyword, an operator;

-Case sensitive;

-End with a semicolon or line break;

-note----code executed by the JavaScript engine is not interpreted

-Single Comment://

-Multiline Comment:/* */

Case sensitive

-Case sensitivity in JavaScript programs

-UserName, UserName, UserName are different

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Summary: This chapter covers JavaScript (overview, basic syntax)

This article from the "Technical Exchange" blog, declined reprint!

JavaScript Basics -1 JavaScript (overview, basic syntax)