🔰compilation

🚧 施工中

JS ⟩ compile

3 stages of compilation：

• lexing: source code -> tokens. (e.g., var a = 2; -> var , a , = , 2 , ; )

• parsing: tokens -> AST (abstract syntax tree).

• code generation: AST -> executable code.

⭐️ 重點

JavaScript code is compiled first, and then execute. (not interpreted line by line)

while scopes are identified during compilation, they're not actually created until runtime (each time a scope needs to run).

compilation

• doesn't do anything in terms of reserving memory for scopes and variables, none of the program has been executed yet.

• creates a map of all the lexical scopes of the program.

runtime

• all the scopes (aka, "lexical environments") and identifiers (variables) for each scope are created at runtime.

📗 參考

• YDKJS: Scope & Closures (v.2) ⟩ Ch. 1: What's the Scope?

• Osman ⟩ Javascript — How the Engine Compiles?

🔴 主題

• stages of compilation：

  • lexing - source code -> tokens.

  • parsing - tokens -> AST

    • ⛔️ early errors - errors on code parsing stage.

  • code generation - AST -> executable code.

• other topics

  • JS is compiled language.

  • LHS reference

  • RHS reference

  • LHS vs. RHS reference

  • hoisting

🗺️ 圖表

3 steps of compilation

🚧

• abstract syntax tree (AST)

• lexical environments