Scientific calculator

It does not use eval, and that is the point

Almost every calculator on the web takes what you type and hands it to eval() or new Function(). Both execute arbitrary JavaScript. It works, it is three lines, and it means the box you type 2+2 into is a box that will run whatever else is put in it — on a page people paste things into from elsewhere.

This one reads the expression properly: it splits it into tokens, rearranges them into reverse Polish notation with the shunting-yard algorithm, and evaluates that over a fixed table of numeric operations. The set of things it can do is the set of things listed above, and nothing typed into it can add to that set. The site's Content Security Policy blocks eval outright as well, so an eval-based calculator would not even run here.

Things it gets right that catch people out

• -3^2 is -9, not 9. The minus applies to the result of the power. Write (-3)^2 for 9.
• 2^3^2 is 512, not 64 — powers group right to left, so it is 2^(3^2).
• 2(3+4) is 14. Implicit multiplication works, which is what you would write on paper and what eval would refuse.
• 0.1 + 0.2 shows 0.3. Binary floating point actually gives 0.30000000000000004; the display rounds to twelve significant figures, which hides the noise without hiding anything real.
• 7 mod 3 is 1, and 50% on its own is 0.5.

Degrees or radians

It starts in radians, which is what every programming language and every calculus course uses. The RAD button switches to degrees if that is what your question is in — and it converts both ways, so asin(0.5) gives 30 in degree mode and 0.5236 in radians.

Questions

Can I type a whole expression?

Yes. Type something like 2(3+4)^2 - sqrt(16) straight into the display and the answer updates as you type. Brackets, implicit multiplication such as 2pi, and scientific notation such as 2.5e-3 all work.

Can I use my keyboard?

Yes — type straight into the display. The keypad exists for phones. Enter puts the current line on the tape above.

How do I switch between degrees and radians?

The RAD button above the keypad toggles it. It starts in radians, which is what every programming language and every maths course uses by default; press it once for degrees.

Why is -3^2 negative nine and not nine?

Because the minus sign applies to the result of the power, not to the 3. -3^2 means -(3^2) = -9. If you want the square of negative three, write (-3)^2, which gives 9. That is the convention in written maths and in scientific calculators; spreadsheets are the well-known exception, where =-3^2 gives 9.

Does this calculator use eval?

No, and that is deliberate. Most browser calculators pass what you type to eval or new Function, which executes arbitrary JavaScript. This one tokenises the expression, converts it to reverse Polish notation and evaluates it over a fixed table of numeric operators, so there is no path from a typed string to executed code. The site's Content Security Policy blocks eval outright in any case.

Is anything sent anywhere?

No. It runs in your browser, there is no history sent anywhere, and nothing is stored.

Why does it not have a graph?

Because doing graphing properly is a much bigger job than doing it badly, and a bad one helps nobody. If you would use it, say so and we will look at it.

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