TypeScript type checking example

TypeScript Basic: Exercise-4 with Solution

Write a TypeScript program that declares a variable as a number and then tries to assign a string to it to see type checking in action.

Sample Solution:

TypeScript Code:

// Declare a variable as a number
let n: number = 42;

// Attempt to assign a string to the number variable (Type Error)
n = "Hello, TypeScript!"; // This line will result in a type error

// Attempt to print the value (won't reach this line due to the error above)
console.log("n = ", n);

Explanations:

In the exercise above -

• First, declare a variable 'n' and explicitly specify its type as 'number' by using the 'number' type annotation.
• We then attempt to assign a string value "Hello, TypeScript!" to the 'n' variable. This is a type mismatch because we're trying to assign a string to a variable declared as a number.
• TypeScript's type checking will catch this error and prevent the program from running successfully.
• Therefore, the console.log statement won't be reached due to the type error.

Output:

Error: Type 'string' is not assignable to type 'number'.

TypeScript Editor:

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

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