➕instanceof

`obj instanceof SomeClass`

JS ⟩ statement ⟩ expression ⟩ operator ⟩ relational ⟩ instanceof

check if SomeClass.prototype is in the prototype chain of obj.

obj instanceof SomeClass

🌟 table of operators

⭐️ 重點

• if obj is not an object, instanceof returns false.

• if SomeClass is not a class/function, it throws a TypeError.

👥 相關

• prototype chain

• "pure" object

💈範例

• replit： "instanceof"

let d = new Date();
let a = [1, 2, 3];
let o = Object.create(null);    // ⭐ pure object

function F(){}

d instanceof Date,    // true
d instanceof Object,  // true
d instanceof Number,  // false

a instanceof Array,   // true
a instanceof Object,  // true
a instanceof RegExp,  // false

o instanceof Object,  // false❗
1 instanceof Object,  // false (1: not an object)
{} instanceof F,      // false

{} instanceof {},     // ⛔ TypeError
//            ^^
// TypeError: Right-hand side of 'instanceof' is not callable

{} instanceof 8,      // ⛔ TypeError
//            ^
// TypeError: Right-hand side of 'instanceof' is not an object

📗 參考

• JavaScript: The Definitive Guide ⟩

  • 4.9.3 The in Operator

  • 6.3.2 Inheritance

📘 手冊

• instanceof