JavaScript Basic Learning-javascript authoritative guide -3.4null and undefined

Null and undefined comparisons

Null is a JavaScript keyword that represents a non-object.

Undefined indicates that there is no value, indicating that the value does not exist or is not initialized.

Same point	Different points
Own type unique value	Null is an object, undefined is a reserved word
No properties and methods	Null is converted into a 0,undefined in a mathematical operation that cannot be transformed or converted into Nan.
= = Think equal, = = =	Null!==undefined//true
are false values, the Boolean variable represents the same value	Null is an empty object, undefined is a property of window (but not an object property)
	Alert (typeof null)//object; Alert (typeof undefined)//undefined;

JavaScript Basic Learning-javascript authoritative guide -3.4null and undefined