Truthy and Falsy
As well as a type, each value also has an inherent boolean value, generally known as either truthy or falsy. Some of the rules are a little bizarre so understanding the concepts and effect on comparison helps when debugging JavaScript applications.
The following values are always falsy:
- false
- 0 (zero)
- '' or "" (empty string)
- null
- undefined
- NaN (e.g. the result of 1/0)
Everything else is truthy. That includes:
- '0' (a string containing a single zero)
- 'false' (a string containing the text “false”)
- [] (an empty array)
- {} (an empty object)
- function(){} (an “empty” function)
Unexpected situations can occur when comparing truthy and falsy values using the == loose equality:
See the Loose Equality Comparison Table
