The difference between 'undefined' and 'null' in JavaScript

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In JavaScript, undefined means a variable has been declared but has not yet been assigned a value, such as:

 var TestVar;
 alert(TestVar); //shows undefined
 alert(typeof TestVar); //shows undefined
null is an assignment value. It can be assigned to a variable as a representation of no value:

 var TestVar = null;
 alert(TestVar); //shows null
 alert(typeof TestVar); //shows object
From the preceding examples, it is clear that undefined and null are two distinct types: undefined is a type itself (undefined) while null is an object.

 null === undefined // false
 null == undefined // true
 null === null // true
and

 null = 'value' // ReferenceError
 undefined = 'value' // 'value'

Second thought tho, null is assigned intentionally, but undefined is not.