🔰short-circuiting

JS ⟩ statement ⟩ expression ⟩ operator ⟩ term ⟩ short-circuiting

a && b               // b may not be evaluated
a ?? b               // (same)
condition ? a : b    // only one of a and b is evaluated
obj ?. prop          // prop may not be evaluated
f ?. (args)          // args expressions may not be evaluated

🌟 table of operators

🔴 主題

• logical operator (&&, ||) - a && b, a || b

• nullish coalescing (??) - a ?? b

• conditional operator (?:) - condition ? a : b

• optional chaining (?., ?.[]) - obj ?. prop, obj ?. [prop]

• optional invocation ?.() - f ?. (args)

💈範例

replit：short-circuiting (optional invocation)

let f = null;      // ⭐ not a function
let x = 0;

try { 
    // 1. `x++` evaluated first. ⭐ 
    // 2. TypeError: f is not a function ⛔ 
    f(x++);     
} catch(e) { 
    log(e.name, e.message);
    log(x);        // 1 (x is incremented)
} 

// ⭐ short-circuiting (`x++` not evaluated)
f ?. (x++),        // undefined (no error)
x,                 // 1 (x not incremented)

📘 手冊

• Operator precedence ⟩ short-circuiting

📗 參考

• JavaScript: The Definitive Guide ⟩ 4.5.1 Conditional Invocation