undefined 🔗
In Javascript undefined (a primitive type in Javascript) gets assigned to a variable that we declare but don’t assign a value to. It’s Javascript’s way of telling that the value of this variable is not defined.
Even a function in Javascript which does not return anything, will return undefined by default.
So, to avoid any error we should never assign undefined to a variable manually.
typeof undefined;
outputs: undefined;
null 🔗
Unlike undefined, null (another primitive type in Javascript) is used when we want to manually or intentionally set the value of a variable to be empty.
When comparing null with undefined remember to use === instead of ==, reason being
null == undefined
returns true as it doesn't check for the type and performs type-conversion
null === undefined;
return false;
typeof null
is object and not null
(more details here)