TypeScript Types

Describe values before runtime.

TypeScript

function greet(name: string): string {
  return `Hello, ${name}`;
}
console.log(greet("Ada"));

Output

Hello, Ada

Explanation

Type annotations let the compiler check how values are used. TypeScript erases annotations when generating JavaScript.

Explore the dry run

Guided walkthroughReady

1function greet(name: string): string {

2 return `Hello, ${name}`;

3}

4console.log(greet("Ada"));

Start to inspect the source, values, and output. These prepared steps explain the published sample; grouped loop steps describe multiple iterations.

View the complete dry-run table

Prepared trace of the published program. Some rows group repeated iterations.
What happens	State after step	Output so far
The type annotations are checked and removed during compilation.	`—`	—
Call greet with Ada.	`name = "Ada"`	—
Build and return the greeting string.	`return = "Hello, Ada"`	—
Write the result.	`return = "Hello, Ada"`	Hello, Ada