🔰converting objects

JS ⟩ value ⟩ object ⟩ convert

convert an object to other forms.

obj.toString()          // object -> string
obj.toLocaleString()    // localization
obj.valueOf()           // object -> primitive (typically, number)
obj.toJSON()            // customization method used by JSON.stringify()

⭐️ 重點

about .toJSON()

• Object.prototype does not define.toJSON().

• JSON.stringify() looks for .toJSON() on any object it is asked to serialize.

• if it exists, it is invoked, and the return value is serialized, instead of the original object.

🔴 主題

• serializing objects

• object -> primitive conversion

  • Ⓜ️ .toString()

  • Ⓜ️ .valueOf()

  • 💾 valueToString()

👥 相關

• type conversion

💈範例

• replit ⟩ .toJSON()

let point = {
    x: 1, y: 2,
    toJSON() { return `(${this.x}, ${this.y})` }    // custom .toJSON() method
};

JSON.stringify([point]),    // '["(1, 2)"]'

📗 參考

• JavaScript: The Definitive Guide ⟩

  • 3.9.2 Explicit Conversions

  • 6.9 Object Methods

  • 14.4.7

📘 手冊

• .toString() ⟩

  • Object.prototype.toString()
• .toLocaleString() ⟩

  • Object.prototype.toLocaleString()
  • Date.prototype.toLocaleString()
• .valueOf() ⟩

  • Object.prototype.valueOf()
• .toJSON() ⟩

  • Date.prototype.toJSON()