Truthy and falsy values in javascript

JavaScript has six different primitive data types:

• Undefined (a variable with no defined value)
• Null (a single null value)
• Boolean (true or false)
• Number (this includes Infinity and NaN – not a number!)
• String (textual data)
• Symbol (a unique and immutable primitive new to ES6/2015)

Everything else is an Object — including arrays.

But, as well as a type, each value also has an inherent boolean value, generally known as either truthy or falsy.

The following values are always falsy:

• false
• 0 (zero)
• '' or "" (empty string)
• null
• undefined
• NaN

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)