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What is grammar?

Grammas are the language of languages. A grammar defines a language. Behind every language, there is a grammar that determines its structure.

Context-free grammar

In computer science, the most common type of grammar is the context-free grammar. Context-free grammars have sufficent richness to describle the recursive syntactic structure of many languages.

Components of a context-free grammar.

A set of rules is the core components of a grammar. Each rule has two parts: (1)a name and (2) an expression of the name. For instance, if we were creating a grammar to handle english text, we might add a rule like: noun-phras may expand into article noun

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1 Overview

JavaScript has had modules for a long time. However, they were implemented via libraries, not built into the language. ES6 is the first time that JavaScript has built-in modules.

ES6 modules are stored in files. There is exactly one module per file and one file per module. You have two ways of exporting things from a module. These two ways can be mixed, but it is usually better to use them separately.

1.1 Multiple named exports

There can be multiple named exports:

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prototype

The prototype is a property of a function_{constructor function} or class_es6. It used for define class's members, like fields and methods, and it's instance(new) will inherit these members. When an instance calls the members it inherited from a class, it dosent look for it's prototype, beacuse an instance dosent has prototype property. What are the members come form? The __proto__ do this, so we talk about 'protorype chain' more likes __proto__.__proto__.__proto__ than protorype.protorype.protorype, the instance.__proto_ === class.prototype is true. we find members from it! So what the prototype is? from the above, we know when we create a instance, the __proto__ will refers to prototype object, we also can say it is used for create __proto__