➕in

`prop in obj`

JS ⟩ statement ⟩ expression ⟩ operator ⟩ relational ⟩ in

// ⭐️ check if `prop` is property of `obj` (including inherited)
prop in obj        // ⭐️ prop: string-convertable expression

🌟 table of operators

👥 相關

• ⚖️ for-in vs. for-of vs. in

💈範例

replit： "in" operator

let point = {x: 1, y: 2};
let array = [1, 2, 3];

'x' in point,            // true
'z' in point,            // false
'toString' in point,     // true    (inherited)

'0' in array,            // true
1 in array,              // true    (1 -> '1')
3 in array,              // false   (3 -> '3', no such prop)
'toString' in array,     // true    (inherited)

📗 參考

• JavaScript: The Definitive Guide ⟩ 4.9.3 The in Operator

📘 手冊

• in operator