Null checking

Explicit null checking

To check if a value is specifically undefined or specifically null you just use the term you want to check for:

p`undefined`(0); // false
p`undefined`(undefined); // true
p`null`(null); // true
p`null`(undefined); // false

p`null`(undefined); // false

To check if a value is not null or undefined you can use the extant operator _:

p`_`(0); // true
p`_`(null); // false
p`_`(undefined); // false
p`_`(NaN); // true

You can always reverse the polarity using the boolean not operator to specifically test for null or undefined:

p`!_`(null); // true

or you can be explicit:

p`null|undefined`(null); // true
p`null|undefined`(0); // false

p`_`(0); // true

if you want to do boolean coercion you can use the boolean coercion (falsey) operator:

p`!`(null); // true
p`!`(undefined); // true
p`!`(NaN); // true
p`!`(0); // true

p`!`(null);

Checking for empty things works as you would expect:

p`[]`([]); // true
p`{}`({}); // true
p`""`(""); // true
p`undefined`(undefined); // true
p`null`(null); // true

p`[]`([]); // true