Type coercion is JavaScript’s implicit type conversion — when JavaScript automatically converts a value to another type during operations.

Coercion happens everywhere in JavaScript. Understanding it is essential to avoid bugs that seem like magic.

Coercion is like a restaurant that adapts your order. You ask for “2” beers (string), and the waiter brings 2 beers (number). It’s convenient, but sometimes you get something unexpected.

flowchart TD
    A["'5' - 3"] --> B["2 (number)"]
    C["'5' + 3"] --> D["'53' (string)"]
    E["'5' * '2'"] --> F["10 (number)"]
    G["!'hello'"] --> H["false (boolean)"]

// String coercion with +
'5' + 3;     // '53'
'5' + true;  // '5true'
'5' + null;  // '5null'

// Number coercion with -, *, /
'5' - 3;     // 2
'10' * '2';  // 20
'10' / '2';  // 5

// Boolean coercion
if ('hello') {}  // truthy
if (0) {}        // falsy
!'hello';        // false
!!'hello';       // true

5 == '5';     // true
0 == false;   // true
'' == false;  // true
null == undefined; // true

• Use === and !== instead of == and !=
• Be explicit with conversions — don’t rely on coercion
• Use Number.isNaN() instead of global isNaN()

[] == false;  // true — surprising!
[] == ![];    // true — the famous JavaScript wtf

• Coercion is implicit type conversion
• + prefers string concatenation
• -, *, / prefer numeric conversion
• Always use === to avoid coercion surprises

• MDN: Type Coercion
• JavaScript Weird Parts — Coercion