Deep understanding of JavaScript - what is JavaScript

Brendan Eich spent 10 days designing a finished language. It's a hodgepodge of references to multiple languages, such as:

• Basic syntax: borrowing from C and Java languages
• Data structures: borrowing from the Java language, including dividing values into primitives and objects
• Usage of functions: borrowing from Scheme language and Awk language, treat functions as first-class citizens, and introduce closures
• The prototypal inheritance model: borrowing from the Self language (a variant of Smalltalk)
• Regular expressions: borrowing from the Perl language
• String and array processing: borrowing from the Python language

At the same time, it is a dynamic, weakly typed programming language that is well suited for object-oriented and functional programming styles

Dynamic languages, corresponding to static languages, static languages determine the data type of variables at compile time; while dynamic languages determine the data type at runtime

Strong typing and weak typing, a strongly typed language cannot be converted once the type of the variable is determined, and the variable type of the weak type is determined by the application context

Features

Based on prototypal inheritance, that is, each object has a prototype object, and the object uses its prototype as a template to inherit methods and properties from the prototype. A prototype object is also an object, also has a prototype, and inherits methods and properties from its prototype, such types, forming a prototype chain. We will introduce the prototype and inheritance in detail later.

Functions are first-class citizens, and can not only be used like objects, but also have functions passed by value and returned as return values. We also introduce later

Function scope, function scope is lexical scope, which can form closures, we will continue later

what is it composed of

JavaScript = ECMAScript + Document Object Model (DOM) + Browser Object Model (BOM)

ECMAScript: The language itself, consisting of syntax, types, statements, keywords, reserved words, operators, global objects

Document Object Model (DOM): API for manipulating HTML, with many and long names, you can check the documentation - MDN

Browser Object Model (BOM): APIs for manipulating browsers, such as Window, Screen, Location, History, Navigator, Popup, Timing, Cookies

ECMAScript version

time point	Version
1997.7	ECMAScript 1.0 released
1998.6	ECMAScript 2.0 released
1999.12	ECMAScript 3.0 released
2007.10	ECMAScript 4.0 draft released, disagreements
2008.7	Improve some 4.0 functions and release ECMAScript 3.1
2009.12	ECMAScript 5.0 officially released
2011.6	ECMAScript version 5.1 released
2013.12	ECMAScript 6 draft released
2015.6	ECMAScript 6 officially released and renamed "ECMAScript 2015"

Since then, a version will be released every year, and the year will be released in that year. For example, if it is released in 2022, it will be called "ECMAScript 2022", and in 2023, "ECMAScript 2023" will be released.

References

• "Review" So what exactly is JavaScript? I was stunned
• History of the JavaScript Language