Your first program

Hello main.ts

A TypeScript program is a plain text file with the ts extension. Open any text editor, type the two lines below, and save them as main.ts in an empty folder.

const message: string = "Hello, TypeScript"; console.log(message);

The first line stores text in a constant typed as string. The second line prints that constant to the terminal.

tsc main.ts

Compile the file by passing its name to tsc. A silent terminal means success: the compiler creates main.js next to main.ts and prints nothing at all.

tsc main.ts

Open main.js to see the result. The output is plain JavaScript with the string annotation erased, ready for any JavaScript runtime.

node main.js

Run the compiled file with node. TypeScript work ends at compile time, so from here on plain node executes the emitted JavaScript:

node main.js

Hello, TypeScript

The terminal prints Hello, TypeScript and nothing else. That short loop of edit, compile, and run drives every lesson that follows.

Read the first error

Break the program on purpose to meet the compiler. Replace the text with a number and compile again:

const message: string = 42;

main.ts(1,7): error TS2322: Type 'number' is not assignable to type 'string'.

Read the message from left to right. It names the file, the line and column in brackets, and the reason: a number was stored where a string was promised.

Fix the line, run tsc main.ts again, and confirm the terminal goes silent. That rhythm of reading the first error and fixing it is the core TypeScript skill.

Next: tsconfig.json

Article author: Arthur Isaev