Challenge 2: Functions

Build a calculation by writing type-safe functions.

Challenge 2: Functions

In this challenge you will write type-safe functions. You will write two functions with explicit parameter and return types: isEven, which checks whether a number is even, and grade, which converts a score to a letter grade.

Exercise isEven function

Write a function isEven(n: number): boolean. Return true if n is even, false if odd. Print the results of isEven(4) and isEven(7).

Show example solution

function isEven(n: number): boolean {
  return n % 2 === 0;
}

console.log(isEven(4));
console.log(isEven(7));

Exercise grade function

Write a function grade(score: number): string. Return "A" for 90 and above, "B" for 80-89, "C" for 70-79, and "F" otherwise. Print the results of grade(95) and grade(65).

Show example solution

function grade(score: number): string {
  if (score >= 90) {
    return "A";
  } else if (score >= 80) {
    return "B";
  } else if (score >= 70) {
    return "C";
  } else {
    return "F";
  }
}

console.log(grade(95));
console.log(grade(65));

Test yourself

In the definition function isEven(n: number): boolean, what does : boolean specify?
- The function name
- The parameter type
- The error type
- The return type
Show answer

The return type — The : boolean after the parameter is the return type. It guarantees the function returns a boolean value.

Complete the return type

function double(x: number): ____ { return x * 2; }

Show answer

function double(x: number): number { return x * 2; }

Function parts

(n: number): boolean

Takes number, returns boolean
n % 2 === 0

Even number check
(score: number): string

Takes number, returns string
return "A"

Returns a string value

Next lesson: Challenge 3: Unions

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