In this tutorial post we are going to discuss the following datatype keyword Null and Undefined. We will see the difference between these datatypes when it comes in use. Before that we'll undersatand concept of null, undefined, zero, Non-Zero. Here we'll see how they are differ to each other. We'll explain that with a example of toilet tissue holder.
Null is a special type in TypeScript that is used to define absence of a value or it is an empty value.Variable declared and is an empty value. It accepts only one value which is null. The variable to represent no value it is an object.
Suppose we are developing an application and showing employee list with first, middle and last name. So many employees don't have a middle names. So in such a case its better to assign the value null to the middle name variable.
// Null Keyword var CheckNull = null; console.log(CheckNull); //output- null console.log(typeof(CheckNull)); //output- object CheckNull=0; // Assigned Zero console.log(CheckNull); //output- Zero let Addnumber:number=CheckNull + 8 // Premitive operation console.log(Addnumber); //output- Zero
Undefined is also a special type in TypeScript that is used to define missing of a value or it is an empty value. Variable has been given a space in memory, but no value is assigned to it. This type we can not used as assign value.
Suppose we are developing an application and showing employee list with first, middle and last name. So many employees don't have a middle names. So in such a case middle name variable of your person object and it has the value undefined. He wouldn't know if the developer forgot to initialize this variable.
//Undefined Keyword var UndefinedNull; console.log(UndefinedNull); //output- undefined console.log(typeof(UndefinedNull)); //output- undefined UndefinedNull=NaN; // Assigned Zero console.log(UndefinedNull); //output- Zero let UndefinedAddnumber:number=CheckNull + 8 // Premitive operation console.log(UndefinedAddnumber); //output- Zero
The main difference between Null and Undefined are as following:
|1||Null must be assigned to a variable.||The default value of any unassigned variable is undefined.|
|2||Null is the intentional absence of a value||Undefined is the unintentional absence of a value|
|3||It is an object type.||it is type undefined.|
|4||Null is converted to zero while performing primitive operations.||Undefined is converted to NaN while performing primitive operations.|