Calculator in your terminal

2025-08-15

2025-10-12 Updated

Save the calculator source code. And start a NodeJS REPL:

node --require ./calc.js

Shortcut

To avoid having to retype the command, create an alias for it in your POSIX terminal profile. Use a full path so that the command works from any working directory.

~/.bashrc

alias calc="node --require ~/scripts/calc.js"

Rationale

The idea here is to use NodeJS as a predictable calculator. You may just use node and leave it at that. But to cut down on keystrokes, we can include a script with useful global properties, such as Math functions or conversion factors. There will always be a clear history of what happened in the scrollback, especially if we avoid mutating variables. You won't quite have the convenience of the last answer, e.g. * 2, but you can quickly retrieve previous expressions with the up arrow or store values with const or let. We can also rename things, e.g. Math.log() might be more familiar as ln() to be clear that it is the natural logarithm and to reserve log() for console printing.

To inspect your global values at runtime, you may enter global or help. To just see names, tab-tab.

Uses

Trigonometry is a good use for a calculator. Here is a function to use the popular 360-degree system:

global.sin = Math.sin
global.sindeg = (a) => sin(tau * a / 360)
global.tau = 2 * Math.PI

What about floating point issues? You can of course choose to ignore them, or you may make use of toPrecision, which we can define as something shorter like pr() or pr1(). In fact, we might as well define 16 at once.

global.pf = Number.parseFloat // string to number
global.pr = (d, x) => x.toPrecision(d)
global.pr1 = pr.bind(null, 1)
Array(16).fill().forEach((_,i) =>
  global[`pr${i+1}`] = pr.bind(null, i+1)
)
global.sci = x => x.toExponential() // scientific notation

I tend to do the raw calculation first, and then adjust for significant figures (or any other desired precision) if the result turns out ugly. Furthermore, we may render a number in scientific notation with sci() or convert a string back to a number with pf().

> .1+.2
0.30000000000000004
> (.1+.2).toPrecision(1)
'0.3'
> pr(1, .1+.2)
'0.3'
> pr1(.1+.2)
'0.3'
> sci(pr1(.1+.2))
'3e-1'
> pf(pr1(.1+.2))
0.3

Convert temperatures between Fahrenheit and Celsius with a precision of 3:

global.fc = (x) => (x - 32) * 5/9
global.fc3 = (x) => pr3(fc(x))

> fc(70.5)
21.38888888888889
> fc3(70.5)
'21.4'

Unit conversion

Factors are stored for unit conversion, especially from U.S. units to metric, however you can go in reverse. Be aware that many units of volume are converted to liters l or milliliters ml, but a liter is only 1e-3 m**3. Due to the lossy nature floating point numbers, I've chosen to focus on values closer to zero when possible to retain precision. Since multiplication is one character, *, it is easier to use than function calls, since you don't have to type parentheses. Division might be apropos for dimensional analysis, but I prefer multiplication and putting numbers alongside their units. Provided are some shorter forms for frequent typing and longer forms that make it more clear what values represent.

global.lfloz = global.floz_per_l = 33.814023
> 2*lfloz
67.628046
> 2 * floz_per_l
67.628046
> 2 / l_per_floz
67.628046
> pr3(2 * floz_per_l)
'67.6'

> (67.5 * l_per_floz)
1.9962132278670301
> (67.5 / floz_per_l)
1.9962132278670304
> pr3(67.5 * flozl)
'2.00'
> pf(pr3(67.5 * flozl))
2

File approach

If you're curious how other commands work, they are stored in files without an extension in a directory listed in the PATH environment variable. The Free Desktop standard recommends using a hidden folder in your home directory.

~/.local/bin/calc

node --require ~/scripts/calc.js

~/.bashrc

export PATH=$HOME/.local/bin:$PATH

Alternatives