Numbers and math

lesson 1-2 · ~8 min · 2/29

One number type

Nearly every program computes something — prices at checkout, scores in a game, minutes left on a timer — so arithmetic is the first tool to move over from Python. The good news: it transfers almost unchanged, with one operator missing and one type merged.

Python has separate int and float types. JavaScript has just one: number. Both 5 and 5.5 are numbers, and division always gives you the exact decimal result.

The operators match Python almost exactly:

Operation	Python	JavaScript
add, subtract, multiply	`+ - *`	`+ - *`
division	`/`	`/`
remainder (modulo)	`%`	`%`
power	`**`	`**`
floor division	`//`	`Math.floor(a / b)`

The one to remember: JavaScript has no // operator. To divide and drop the decimal part, divide normally and round down with Math.floor(...).

Code exercise · javascript

Predict each line before you run it. The third line is the remainder of 7 divided by 2, and the last uses Math.floor to copy Python's 7 // 2.

The Math toolbox

Math is a built-in object full of helpers, like Python's math module but always available with no import:

Math.floor(3.9) → 3 (round down)
Math.round(3.5) → 4 (round to nearest)
Math.abs(-8) → 8 (absolute value)
Math.max(2, 9, 4) → 9 and Math.min(2, 9, 4) → 2
Math.sqrt(81) → 9 (square root, √81)

You call them with a dot, Math.floor(x), because they live on the Math object. Objects get a full treatment in unit 5.

Code exercise · javascript

Your turn. A timer holds 400 seconds. Print the whole minutes (400 divided by 60, rounded down) on the first line and the leftover seconds (the remainder) on the second line.

Code exercise · javascript

Second practice. A restaurant bill is 50 and the tip rate is 0.2 (20%). Print the tip amount on the first line and the bill plus tip on the second, using math on the two variables (no hand-typed answers).

Quiz

In Python, 7 // 2 gives 3. Which JavaScript expression gives the same result?