❗sloppy mode

JS ⟩ concepts ⟩ environment ⟩ JS engine ⟩ mode ⟩ sloppy

🈯 synonyms： "non-strict mode", "sloppy mode"

👉 compare： strict mode

⭐️ 重點

in sloppy mode：

• although scopes are determined at compile-time, you can modify the scope at runtime❗ ( 👉 modify current scope at runtime❗️❗)

• function in block (FiB) is hoisted / initialized to undefined (outside the block)❗

• assignment (=) to undeclared identifier will result in accidental global variable in sloppy mode❗️

JS is lenient with var, strict with let.

• var redeclaration applied even in strict mode❗️, even in strict mode❗

• let redeclaration not allowed even in sloppy mode❗️, even in sloppy mode❗

with a function in block (FiB)

• sloppy mode: ✅ hoisted / initialized to undefined (in outer scope)

• strict mode: ⛔ ReferenceError (invisible in outer scope)❗

🔴 主題

• accidental global variable in sloppy mode❗️❗

• modify current scope at runtime❗️❗

🖥️ 影片

📘 手冊

• Strict mode

• Sloppy mode