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JavaScript Truthy and Falsy

المعرفة:: JavaScript
الحالة:: ملاحظة_مؤرشفة
المراجع:: https://developer.mozilla.org/en-US/docs/Glossary/Falsy, https://developer.mozilla.org/en-US/docs/Glossary/Truthy, The Complete JavaScript Course 2022 From Zero to Expert

Falsy

A falsy (sometimes written falsey) value is a value that is considered false when encountered in a Boolean context.

Value Description
false The keyword false.
0 The Number zero (so, also 0.0, etc., and 0x0).
-0 The Number negative zero (so, also -0.0, etc., and -0x0).
0n The BigInt zero (so, also 0x0n). Note that there is no BigInt negative zero — the negation of 0n is 0n.
”“, ‘’, `` Empty string value.
null null — the absence of any value.
undefined undefined — the primitive value.
NaN NaN — not a number.
document.all Objects are falsy if and only if they have the IsHTMLDDA internal slot.That slot only exists in document.all and cannot be set using JavaScript.

In short:

  • 0
  • "" (Empty String)
  • undefined
  • null
  • NaN

Examples of falsy values

if (false)  
if (null)  
if (undefined)  
if (0)  
if (-0)  
if (0n)  
if (NaN)  
if ("")

Truthy

In JavaScript, a truthy value is a value that is considered true when encountered in a Boolean context. All values are truthy unless they are defined as falsy. That is, all values are truthy except false, 0, -0, 0n, "", null, undefined, and NaN.

Note: Empty Objects {} and Arrays [] aren’t falsy!

Examples of truthy values

if (true)  
if ({})  
if ([])  
if (42)  
if ("0")  
if ("false")  
if (new Date())  
if (-42)  
if (12n)  
if (3.14)  
if (-3.14)  
if (Infinity)  
if (-Infinity)
Last update : August 14, 2023
Created : August 23, 2022

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