TypeScript User Input

readLine fills a variable

readLine() reads the next line from the stdin box at/typescript/try. It returns a string. Store that string, or convert it with Number when you need a number. This is StudyGrid’s input, not prompt() and not C++ cin.

declare function readLine(): string;

console.log("Enter your age:");
const age: number = Number(readLine());
console.log("You entered " + age);

The declare line tells tsc that readLine exists and returns a string. The editor provides the real function when the program runs. Sample stdin for this program: 20.

Always prompt with console.log

A program that waits on readLine() with no message looks frozen. Print a question first so the person at the keyboard knows what to type. On StudyGrid the answer is already in the stdin box before you compile, but the prompt still documents the program.

declare function readLine(): string;

console.log("Price in euros:");
const price: number = Number(readLine());
console.log("Recorded: " + price);

Sample stdin: 3.5. Change it and compile again.

Several values, several calls

Each readLine() takes one line. Call it twice for two values. Put each value on its own line in the stdin box. Spaces inside a line stay in the string; the next call does not start until the next line.

declare function readLine(): string;

console.log("Enter two integers:");
const a: number = Number(readLine());
const b: number = Number(readLine());
console.log("sum is " + (a + b));

Sample stdin for that program: two lines, 4 then 9. The first call gets4. The second call gets 9.

The type must match

readLine() always returns text. Number(readLine()) turns that text into anumber. If the line is hello, the result is NaN (not a number). Ask for the kind of value you declared, and test with matching stdin.

A whole line, including spaces

readLine() reads until the end of the line. Spaces stay in the string. That is closer to C++getline than to cin >>, which stops at the first space. For a full name such asAda Lovelace, one call is enough.

declare function readLine(): string;

console.log("Type a name:");
const name: string = readLine();
console.log("Hello, " + name);

Output asks, input answers

console.log writes. readLine reads. Most interactive programs are that pair, repeated. Next: the types you can store in those variables.