null is written with a literal,
null (it's not an identifier for a property of the global object like
undefined can be). In APIs,
null is often retrieved in place where an object can be expected but no object is relevant. When checking for null or undefined beware of the differences between equality (==) and identity (===) operators (type-conversion is performed with the former).
// foo does not exist. It is not defined and has never been initialized: > foo "ReferenceError: foo is not defined" // foo is known to exist now but it has no type or value: > var foo = null; foo "null"
typeof null // object (bug in ECMAScript, should be null) typeof undefined // undefined null === undefined // false null == undefined // true
|ECMAScript Language Specification |
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