Types, operators & formatting

Numbers that make sense

Lesson 3 of 20 · 8 min · Module 1: Values & first steps

A value has a type, and its type changes what an operation means. Numbers can be calculated; strings can be joined.

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By the end, you’ll be able to…

Distinguish numbers from strings
Use arithmetic and string concatenation
Format a value without changing its numeric source

The idea

The expression 2 + 3 is 5, while "2" + "3" is "23". A number’s toFixed(2) method returns a string with two decimal places.

const price = 12.5;
console.log("EUR " + price.toFixed(2)); // EUR 12.50

01Keep calculation and presentation separate

Calculate using numbers first. Convert the result to display text only at the boundary where a person needs to read it. Formatting is a presentation step, not a new numeric type.

const subtotal = 5 * 3;
const label = subtotal.toFixed(2);
console.log(typeof subtotal, typeof label);

Output

number string

02Read a method call

In price.toFixed(2), price is the value, toFixed is the operation, and 2 is the requested number of decimal places. The method returns a new string; it does not replace price. The supplied function formatPrice(price) is a reusable recipe: calling formatPrice(12.5) gives price the value 12.5. Use return to send the formatted string back to that caller.

Your turn

Write formatPrice(price) to return a string starting with "EUR ", followed by the price with exactly two decimal places.

What the checks look for

Formats a decimal price
Keeps two decimal places for whole numbers
Handles zero

Try it in the editor →

Take this with you

Choose the right type for the operation, then format the result for display.