🔢Infinity

• JS ⟩ value ⟩ primitive ⟩ number ⟩ special ⟩ Infinity

• JS ⟩ scope ⟩ global ⟩ global object ⟩ property ⟩ Infinity

( global object property )❗

• a property of the global object. (that is, a variable in global scope).

• initial value of Infinity is Number.POSITIVE_INFINITY.

• Infinity is greater than any other number.

🈯 synonyms： "positive infinity"

⭐️ 重點

Infinity

• division by zero yields ±Infinity (no error)❗

• converts to 0 when used as operands of bitwise operator.

👥 相關

• 👉 NaN - not a number.

• ⚠️division (/) may result in Infinity❗

💈範例

• replit - JS: ±Infinity & ±0

const M = Number.MAX_VALUE;     // = 1.7976931348623157e+308 ≈ 2¹⁰²⁴
const D = Math.pow(2, 970);     // 2⁹⁷⁰
const d = Math.pow(2, 969);     // 2⁹⁶⁹

// -------- Infinity --------

 1 / 0,     //  Infinity
-1 / 0,     // -Infinity

 Infinity === Number.POSITIVE_INFINITY, // true
-Infinity === Number.NEGATIVE_INFINITY, // true

3 + Infinity,           // Infinity
3 / Infinity,           //  0
-3 / Infinity,          // -0
Infinity / Infinity,    // NaN

// -------- Number.MAX_VALUE --------

M,                      // 1.7976931348623157e+308

// ⭐️ 只要 M 的最後一位 (2⁹⁷¹) 的一半 = 2⁹⁷⁰ 就足以讓 M 「進位」變成 Infinity
M + D,                  // Infinity

// ⭐️ 再小的話，則會被直接「捨棄」。
M + d,                  // M

// -------- Number.MAX_SAFE_INTEGER --------

Number.MAX_SAFE_INTEGER,    // 9007199254740991 = 2⁵³ - 1
Math.pow(2, 53) - 1,        // 9007199254740991

📗 參考

• JavaScript: The Definitive Guide ⟩ 4.8 Arithmetic Expressions

📘 手冊

• Infinity

• Number.POSITIVE_INFINITY