⚖️(~~) vs. Math.trunc()

xJS ⟩ statement ⟩ expression ⟩ operator ⟩ double tilde (~~)

nearest integer towards 0.

// ⭐️ ~~(x) : nearest integer towards 0
//    (almost) same as Math.trunc() = sign(x) * [|x|]
~~(7.8),            //  7
~~(-5.6),           // -5
Math.trunc(7.8),    //  7
Math.trunc(-5.6),   // -5

~~M,                // ❗ 0 (overflow: ~~(x+M) = ~~x)
Math.trunc(M),      // ⭐️ M (Math.trunc() has wider range)

👉 bitwise not (~) | 🌟 2's complement

⭐️ 重點

~~ vs. Math.trunc()：the difference

• Math.trunc(x)

  • will try to convert x with "prefer-number" conversion, if it's NaN, the result remains NaN.

  • has wider range. (see example above)

• bitwise not (~) the following all converted to 0 before applying bitwise not (~) operator.

  • null / undefined / false / "" (empty string) / NaN / Infinity

  • non-numeric String / non-numeric Array

  • other object (except Date)

💈範例

"~~" vs. Math.trunc()

注意：使用 JSON.stringify() 將函數轉換成字串時，會轉成 "undefined"❗️

👥 相關

• bitwise operator ⟩ bitwise not (~) - invert bits.

• unary arithmetic operator ⟩ unary plus (+)

• unary logical operator ⟩ logical not (!)

📗 參考

• CodeWars ⟩ Adding Big Numbers

📘 手冊

• Bitwise NOT (~)

• Math.trunc() - same as ~~ (with wider range)

🗣 討論

• SOF ⟩ What does ~~ ("double tilde") do in Javascript?