What is a JavaScript

This chapter mainly describes the historical development, key evolution nodes and achievements of JS. Although there is no need to study this chapter in depth, it is still necessary to read it, because some of the reasons for the evolution and the disadvantages brought by them are what we need to think about as users. I will focus on mentioning and attaching my thoughts in the following article, hoping to attract various gods to discuss together.

Historical review

  • In 1995, the Mocha (LiveScript) blueprint began.
  • In August 1996 came the Web browser, a developer’s nightmare, and hence the standardization that followed.
  • In 1997, the ECMA-262 language standard was introduced.
  • In 1998, ISO and IEC came up with a standard, ECMA, and browsers had a specification.

The evil Internet Explorer was the first to follow ECMA, but sadly out of date

JavaScript implementation

erDiagram
JavaScript ||--o{ ECMAScript : contain
ECMAScript 
JavaScript ||--o{ DOM : contain
DOM
JavaScript ||--o{ BOM : contain
BOM

The JAVAScript version

Important Nodes fourth edition, strongly typed variables, statements and data structures, real classes, and inheritance. Although changed to ES3.1, JS data manipulation has been more standardized, for the following ES5 JSON, ES6 classes, modules, iterators, arrow functions, contract reflection, proxy and other data structures to pave the way.

Async /await, which is favored by Web developers, was introduced in ES8.

Browser support for ES

IE5 started with version 1 of the specification, but unfortunately there was too little documentation and JScript was not hardcore enough. Subsequently, IE8 was the first to implement version 5.

DOM document object model

  • Advantage:
  • Note: The dom gives the page the concept of hierarchical nodes, making it easier to change nodes.
  • Again, it’s a matter of standards, but the normalization of the DOM keeps the browser specification from falling too far apart
  • Disadvantage:
  • DOM is large and has many properties, especially after DOM LEVEL3, and views, events, styles, traversals, and scopes make DOM large and can easily get stuck because of frequent changes.

WEB browser support for DOM

EI did not support dom new features in 6 and 7, whereas firefox has done a good job of supporting almost all of LEVEL2 in 3+ and is 100% compatible, clap your hands!

BOM Browser object model

  • Navigator objects: Information about your browser, such as Bluetooth, devices, and so on
  • Location object: page information, link, host port number, etc

BOM and DOM will be explained in detail later, especially DOM. After all, I think Internet Explorer failed to pay attention to the evolution of DOM and its status in the mind of developers

conclusion

JS is a scripting language used to interact with pages. It consists of ECMA, DOM and BOM. The increasing standardization of ECMA is a sign of the maturing of a language and the expansion of the platform. In an era of diverse browsers, each has its own place.