Union and intersection types in TypeScript

TypeScript Advance Types: Exercise-1 with Solution

Write a TypeScript program that declares a variable 'result' that can hold either a 'string' or a 'number'. Now write a function that takes an argument of type 'string | number | boolean' and logs its type.

Sample Solution:

TypeScript Code:

// Declare a variable 'result' with a broader union type
let result: string | number | boolean;

// Function that logs the type of the argument
function logType(arg: string | number | boolean): void {
  if (typeof arg === "string") {
    console.log("Type: string");
  } else if (typeof arg === "number") {
    console.log("Type: number");
  } else if (typeof arg === "boolean") {
    console.log("Type: boolean");
  } else {
    console.log("Type: unknown");

// Testing the function with different argument types
result = "TypeScript ";
logType(result); // Output: Type: string

result = 100;
logType(result); // Output: Type: number

result = true; // Assigning a boolean value
logType(result); // Output: Type: boolean


In the exercise above -

  • First, we declare a variable 'result' with the union type string | number | boolean, which means it can hold values of either 'string' or 'number' or 'boolean' types.
  • Define a function "logType()" that takes an argument 'arg' of type string | number | boolean. Inside the function, we use the 'typeof' operator to check the type of arg and log the corresponding type.
  • Finally, we test the "logType()" function by assigning 'result' different values, such as a string and a number, and then calling the function to log their types.


"Type: string"
"Type: number"
"Type: boolean"

TypeScript Editor:

See the Pen TypeScript by w3resource (@w3resource) on CodePen.

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