🔸property name

string or symbol.

JS ⟩ values ⟩ object ⟩ property ⟩ name

(String / Symbol)

a property name may be any String / Symbol.

(any other value is coerced to String.)

// defining properties
{
    age  : 26,                    // normal string property name
    1    : '1 is OK',              // normal string property name
    const: 'reserved word is OK',  // reserved word as property name
    "full name": "John Doe",       // string as property name
}

// accessing properties
obj . prop    // by identifier
obj [ prop ]  // by String / Symbol.

⭐️ 重點

in dot notation (.) obj.prop syntax, the prop：

• must be an identifier❗

• can be a reserved word❗

🔴 主題

• dot notation (.)

• bracket notation []

• computed property name

💈範例

• replit ⟩ property name

// a symbol
let symbol = Symbol('hi');

// an object
let obj = {
    
    // string as property name
    name        : 'normal property names are converted to strings ("name")',
    const       : '⭐ reserved word as property name is OK',
    1           : '⭐ 1 is legal property name, coerced to "1".',
    'full name' : 'string as property name',
    symbol      : 'this `symbol` is a normal string property name ("symbol")',
    
    // symbol as property name
    [symbol]    : 'symbol as property name',    // computed property name
};

obj['full name'],   // 'string as property name'
obj[symbol],        // 'symbol as property name'
obj.symbol,         // 'this `symbol` is a normal string property name ("symbol")'
obj.const,          // '⭐ reserved word as property name is OK'

obj[1],             // ✅ "bracket notation" is always safe.

// obj.1,           // ❗ "dot notation" requires an identifier
//    ^^            // ⛔ SyntaxError: Unexpected number

1 in obj,           // true (1 -> '1')
'1' in obj,         // true (normal string property name)
'name' in obj,      // true (normal string property name)
symbol in obj,      // true (symbol as property name)
'symbol' in obj,    // true (normal string property name)

📘 手冊

• Property accessors - access properties using dot/bracket notation.

  • property name