JavaScript checking for null vs. undefined and difference between == and ===

Question

1. How do I check a variable if it\'s null or undefined and what is the difference between the null and undefined?<

Answer 1

How do I check a variable if it's null or undefined

just check if a variable has a valid value like this :

if(variable)

it will return true if variable does't contain :

• null
• undefined
• 0
• false
• "" (an empty string)
• NaN