🔰for-of with objects

JS⟩ syntax ⟩ for loops ⟩ for-of ⟩ with objects

(by default) object is not iterable❗

let obj = { x: 1, y: 2, z: 3 };
for (let value of obj) { }                 // TypeError

// use Object.keys/values/entries
for (let key of Object.keys(obj) { ... }
for (let value of Object.values(obj) { ... }
for (let [key, value] of Object.entries(obj) { ... }

// or for-in
for (let key in obj) { ... }                

👉 for-in vs. for-of vs. in

⭐️ 重點

the iteration of Object.keys() is not live as the example：arrays are iterated "live"❗️

👥

• iterable

• for-in

• arr.entries

📗

• JavaScript: The Definitive Guide ⟩ 5.4.4 for/of loop

📘

• for...of

• Object ⟩

  • Object.keys()

  • Object.values()

  • Object.entries()

• Object.prototype ⟩

  • .hasOwnProperty()

• "in" operator