*️token

🚧 施工中

JS ⟩ grammar ⟩ token

tokens are：

• keywords (if, else, var ...)

• punctuators (+, -, ? , {, }...)

• identifiers

• literals

🔴 主題

• generating tokens

  • lexing stage (e.g., var a = 2; -> var , a , = , 2 , ; )

• types of tokens

  • keyword

    • reserved word

    • contextual keyword

  • punctuator

    • semicolon (;)

  • identifier

    • identifier vs. keyword

  • literal

⭐️ 重點

tokens are generated from the lexing stage of compilation.

• ... input elements other than white space and comments form the terminal symbols for the syntactic grammar for ECMAScript and are called ECMAScript tokens.

• These tokens are the reserved word, identifiers, literals, and punctuators of the ECMAScript language.

• Moreover, line terminators, although not considered to be tokens, also become part of the stream of input elements and guide the process of automatic semicolon insertion (12.9). 👉 ECMA spec

📗 參考

• Airbrake ⟩ Have a JavaScript Unexpected Token Error? Check Your Syntax

• GitHub ⟩ js-tokens - JavaScript tokenizer.

• ariya.io ⟩ Most Popular JavaScript Tokens (2012)

📘 手冊

• SyntaxError: Unexpected token

• ECMA ⟩ 5.1.2 The Lexical and RegExp Grammars

💈範例

⛔ SyntaxError: unexpected token "xxx"

• replit：JS is a compiled language

var greeting = "Hello";
console.log(greeting);   // ⭐️ this line doesn't have a chance to run❗ 

greeting = ."Hi";        // ⭐️ error occurred in the "tokenizing" stage
//         ↑             //    of compilation❗
//         ↑
// ⛔ SyntaxError: unexpected token .

🚧

• Error

• SyntaxError

• punctuators