How to Get a Variable Type in TypeScript ?

To get a variable type in TypeScript, we have different approaches. In this article, we are going to learn how to get a variable type in Typescript.

Below are the approaches used to get a variable type in TypeScript:

Approach 1: Using typeof Operator

You can use the typeof operator to get the type of a variable at runtime. It returns a string representing the type of the operated variable.

Example: In this example, we are using typeof Operator to get the type of a variable.

Javascript

let myVar: number = 42;
console.log(typeof myVar);

Output:

number

Approach 2: Using instanceof Operator

The instanceof operator checks if an object is an instance of a particular class or type. It can be used to check the type of an object.

Example: In this example, we are using instanceof Operator to get the type of a variable.

Javascript

class MyClass {
    // class definition
}

let myInstance = new MyClass();
if(myInstance instanceof MyClass){
    console.log(`myInstance is an instance
                 of class MyClass and its
                 type is: ${typeof myInstance}`)
}

Output:

myInstance is an instance of class MyClass and its type is: object

Approach 3: Using Type Guards

You can create custom type guards using functions that narrow down the type of a variable based on certain conditions.

Example: In this example, we are using Type Guards to get the type of a variable.

Javascript

function isString(value: any): void {
    if (typeof value === "string") {
        console.log("It's a string!");
    }
    else{
        console.log(`Passed value is
                     of ${typeof age}
                     type.`)
    }
}

let greet: any = "Hello, TypeScript!";
const age: any = 20;

isString(greet);
isString(age);

Output:

It's a string!
Passed value is of number type.