What is Type Coercion in JavaScript? | JavaScript Interview Questions

What You'll Learn

Implicit vs explicit coercion
Truthy and falsy values
== vs === comparison

Type Coercion

JavaScript automatically converts values between types when needed.

Falsy Values

code.jsJavaScript

// All falsy values
false
0
-0
''
null
undefined
NaN

// Everything else is truthy
'0'     // truthy
[]      // truthy
{}      // truthy

Implicit Coercion

code.jsJavaScript

// String coercion
'5' + 3      // '53' (number to string)
'5' - 3      // 2 (string to number)

// Boolean coercion
!!'hello'    // true
!!0          // false

// Comparison
'5' == 5     // true (coercion)
'5' === 5    // false (no coercion)

== vs ===

Operator	Type Coercion	Use Case
==	Yes	Almost never
===	No	Almost always

code.jsJavaScript

null == undefined   // true
null === undefined  // false

[] == false         // true
[] === false        // false

'' == false         // true
'' === false        // false

Explicit Coercion

code.jsJavaScript

Number('5')       // 5
String(5)         // '5'
Boolean(1)        // true
parseInt('10px')  // 10