➕add/concate (+)

number addition / string concatenation.

JS ⟩ operator ⟩ arithmetic ⟩ add / concate (+)

string concatenation or number addition. 👉 table of operators

1 + 2            // number addition 
'the' + 'fox'    // string concatenation

🗺️ 圖表

💈範例

• replit：the + operator

//                   result             conversion
// -------------------------------------------------------------
1 + 2,            // 3
'1' + 2,          // '12'               (2 -> '2')
'1' + '2',        // '12'

1 + {},           // '1[object Object]' ({} -> object to primitive)
true + true,      // 2                  (true -> 1)
2 + null,         // 2                  (null -> 0)
3 + undefined,    // NaN                (undefined -> NaN)

// ❗ `+` mixed with strings and numbers is not associative
// -------------------------------------------------------------
(1 + 2) + ' cats',    // '3 cats'       (addition -> concatenation)
1 + (2 + ' cats'),    // '12 cats'      (2 concatenations)

👥 相關

• ℹ️ object -> primitive conversion is involved in + operation.
• ℹ️ comparison operator favors numbers, + favors strings.
• ℹ️ + operation uses punctuator plus (+).

📗 參考

• JavaScript: The Definitive Guide ⟩ 4.8.1 The + Operator

📘 手冊

• Addition (+)