Runtime type checking strategies in Typescript - Mini Project: Build & Apply

Runtime type checking strategies

📋 What You'll Learn

💡 Why This Matters

🌍 Real World

When working with data from APIs or user input, runtime type checking helps prevent errors by verifying data shapes before using them.

💼 Career

Many jobs require validating external data safely. Knowing runtime type checking strategies in TypeScript is useful for frontend and backend development.

1

Create the user data object

Create a constant object called userData with these exact properties and values: name as "Alice" (string), age as 30 (number), and isMember as true (boolean).

Typescript

// Create the userData object with name, age, and isMember properties
// Your code here

Need a hint?

Use const userData = { name: "Alice", age: 30, isMember: true };

2

Define expected property names

Create a constant array called expectedProps containing the strings "name", "age", and "isMember".

Typescript

const userData = { name: "Alice", age: 30, isMember: true };
// Create expectedProps array with "name", "age", "isMember"
// Your code here

Need a hint?

Use const expectedProps = ["name", "age", "isMember"];

3

Write a runtime type check function

Write a function called isValidUser that takes a parameter obj of type any and returns true if obj has all properties in expectedProps with types string for name, number for age, and boolean for isMember. Otherwise, return false. Use typeof checks inside the function.

Typescript

const userData = { name: "Alice", age: 30, isMember: true };
const expectedProps = ["name", "age", "isMember"];
// Write isValidUser function to check property existence and types
// Your code here

Need a hint?

Check each property with typeof obj.property === "type" and combine with &&.

4

Print the runtime type check result

Write a console.log statement that prints the result of calling isValidUser(userData).

Typescript

const userData = { name: "Alice", age: 30, isMember: true };
const expectedProps = ["name", "age", "isMember"];

function isValidUser(obj: any): boolean {
    return typeof obj.name === "string" &&
           typeof obj.age === "number" &&
           typeof obj.isMember === "boolean";
}
// Print the result of isValidUser(userData)
// Your code here

Need a hint?

Use console.log(isValidUser(userData)); to show the check result.