JavaScript Converting to boolean


Boolean(...) will convert any data type into either true or false.

Boolean("true") === true
Boolean("false") === true
Boolean(-1) === true
Boolean(1) === true
Boolean(0) === false
Boolean("") === false
Boolean("1") === true
Boolean("0") === true
Boolean({}) === true
Boolean([]) === true

Empty strings and the number 0 will be converted to false, and all others will be converted to true.

A shorter, but less clear, form:

!!"true" === true
!!"false" === true
!!-1 === true
!!1 === true
!!0 === false
!!"" === false
!!"1" === true
!!"0" === true
!!{} === true
!![] === true

This shorter form takes advantage of implicit type conversion using the logical NOT operator twice, as described in

Here is the complete list of boolean conversions from the ECMAScript specification

  • if myArg of type undefined or null then Boolean(myArg) === false
  • if myArg of type boolean then Boolean(myArg) === myArg
  • if myArg of type number then Boolean(myArg) === false if myArg is +0, ‑0, or NaN; otherwise true
  • if myArg of type string then Boolean(myArg) === false if myArg is the empty String (its length is zero); otherwise true
  • if myArg of type symbol or object then Boolean(myArg) === true

Values that get converted to false as booleans are called falsy (and all others are called truthy). See Comparison Operations.