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What is typeof operator in typescript?
This operator is used to get a string specifying the type of variable. This will very helpful for developers to know the type of the object at runtime.
typeof operator syntax
typeof {operand}
parameter:
operand is supplied either as the primitive data type of custom object. possible operand values are variables, object variables, and strings.
var msg = "Cloudhadoop";
console.log(typeof msg); // returns string as string format
var variableNumber =16;
console.log(typeof variableNumber); // returns number as string format
var variableBoolean =true;
console.log(typeof variableBoolean); // returns boolean as string format
var variableNull =null;
console.log(typeof variableNull); // returns the object as string format
var variableArray:string\[\]= \["1","2","3","4"\]
console.log(typeof variableArray); // returns object as string format
let variableTyple: \[string, number\]= \["type operator", 20\];
console.log(typeof variableTyple); // returns object as string format
let variableAny: any = 4;
console.log(typeof variableAny); // returns number as string format
let variableUndefined: undefined = undefined;
console.log(typeof variableUndefined); // returns undefined as string format
enum Monday { Sunday, Monday, Tuesday }
let enumVariable: Monday = Monday.Sunday;
console.log(typeof enumVariable); // returns number as string format
var myFunction = new Function('123 + 6');
console.log(typeof myFunction) // outputs 'Function'
var currentDate = new Date();
console.log(typeof currentDate) // outputs 'object'
typescript instanceof operator
instance of operator checks if the object is another object type and returns true. This checking is done at runtime. It checked conditional expressions to check object type.
Syntax
name instanceof type
the name is of an object name and the type is of the object type
instanceOf Examples
In the below code, the date object name checks against Class and returns.
any variable returns false against the date object
var todaysDate = new Date();
var variableNumber: any = 12;
console.log (todaysDate instanceof Date) // returns true
console.log (variableNumber instanceof Date) // returns false
instanceof class example
It returns false if the undefined type-checked with class,
class ClassExample {}
let classes: Array = \[\];
console.log(classes\[0\]); // returns undefined
console.log(classes\[0\] instanceof ClassExample);
//returns false undefined is not of ClassExample
classes.push(new ClassExample());
console.log(classes\[0\]); // outpus empty class
console.log(classes\[0\] instanceof ClassExample); // true
instanceof interface example:
This is an example of usage of the interface with the instanceof operator
interface InterfaceExample { }
var interfaceVariable: InterfaceExample = { };
console.log(interfaceVariable instanceof InterfaceExample); // compilation error
class ClassExample { }
var variableClass: ClassExample = { };
console.log(variableClass instanceof ClassExample); // reutnrs false and no compilation error
as you see interface gives ’ InterfaceExample’ only refers to a type, but is being used as a value here error
Conclusion
To sum up, Learned A Step by Step example for Typescript typeof, instanceOf operator tutorials programs syntax.
