TypeScript type inference example

TypeScript Basic: Exercise-5 with Solution

Write a TypeScript program that declares a variable without specifying its type and shows how TypeScript infers the type based on the assigned value.

Sample Solution:

TypeScript Code:

// Declare a variable without specifying its type
let temp = 100; // TypeScript will infer the type based on the assigned value

// Check the inferred type
console.log("Type of temp:", typeof temp);

// Attempt to reassign the variable with a different type
temp = "Hello, TypeScript!"; // TypeScript will catch this as a type error

// Display the value (won't reach this line due to the error above)
console.log("My Variable:", temp);

Explanations:

In the exercise above -

• First, declare a variable 'temp' without specifying its type explicitly. TypeScript will infer the type based on the assigned value, 100.
• We use typeof to check the inferred type of 'temp' and log it to the console.
• We then attempt to reassign 'temp' with a string "Hello, TypeScript!". TypeScript's type inference will initially set 'temp' as type number, and it will catch a type error when we try to assign a string to it.
• Therefore, the console.log statement for displaying the value 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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