JavaScript learning experience

1. Foreword:

I read the Little Red Book (JavaScript Advanced Programming) some time ago, but I didn’t plan to read it, and I didn’t take detailed notes. After reading it, I felt a little empty and felt something was wrong. It’s hard to remember what I learned, and I don’t have a deep impression. I feel frustrated. I can’t even learn how to do front-end using JS. The backend has learned js, you decide whether to die or not.

So I read it, read it again, and decided to blog about it to enhance my impression and make reading notes for future reading and for everyone's reference and discussion.

Warm reminder: Notes and words will be subjective, and knowledge should be recorded with emphasis.

2. History of JavaScript

• Origin: It is said that in 1995, at the end of the last century, Netscape launched the Navigator browser. The company is pursuing not only static HTML, but also dynamic effects. They also want to be able to handle the verification of the form. Don't always wait until the backend to know whether the form input is legal or not, especially in that era. We waited for minutes at a time, and now we wait for ten seconds without wanting to turn it off, while complaining about some broken website.

• Get started: Just do it if you have a goal. There are many great people at Netscape. Brendan Eich developed JavaScript in 10 days (it says 10 days online). When it first came out, it was called LiveScript, but in order to capitalize on the popularity of the popular star Java, it was changed to JavaScript, so in fact they have nothing to do with each other.

• Competition: Seeing that Netscape has js, Microsoft felt that it was not good and my IE was going to be killed. At the same time, it also felt that js had a bright future, so I made a JavaScript implementation called JScript.

• Standards: The js competition between Netscape and Microsoft has led to version inconsistencies. With industry concerns, the standardization of JavaScript has been put on the agenda. The ECMA organization went to do this, and finally came up with ECMAScript as a standard in 1997. Here ECMAscript and JavaScript can be seen as expressing the same thing

3. ECMAScript

ECMAScript (hereinafter referred to as ES) is formulated by ECMA-262, and ES is mainly about language The basis of grammar is the existence of a standard. If you insist on distinguishing ES and JS, ES is the basic language standard, and JS is the language implemented on the basis of this standard.

About ES versions: ES has gone through many versions since it was formulated in 1997. The previous versions were all minor modifications. Important version:

• ES3, the third version, is the first real modification to the standard

• 2009 ES5 is currently supported by all major popular browsers

• The ES6 published in 2015 has also become popular.

• Versions will be released every year after 2015, but browsers are not yet able to support it.

4. JavaScript implementation

Javascript consists of three parts:

1.ECMAScript: The core part is the grammatical basis of js. We will continue to write about its syntax later.
2.DOM (Text Object Model): Application programming interface for operating HTML documents. About DOM:

• The emergence of DOM makes it possible to implement dynamic HTML (DHTML), which can change the appearance and content of web pages without reloading the page.

• Problems caused by DOM: Mainly in terms of compatibility, Netscape and Microsoft have their own opinions, resulting in browser incompatibility. This problem has not been solved. W3C has started planning DOM

• ##DOM levels: DOM1, DOM2, DOM3. The levels here are equivalent to the DOM versions, which means that DOM is constantly improving. Now the latest is DOM3

3.BOM (browser model): Use BOM to control parts other than the page displayed by the browser

5. JavaScript usage:

(1) Tag attributes: The key to using js in web pages is to use the

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