possible operations
references: https://github.com/silentmatt/expr-eval

operator	description
-x	Negation
+x	Unary plus. This converts it's operand to a number, but has no other effect.
x!	Factorial (x * (x-1) * (x-2) * … * 2 * 1). gamma(x + 1) for non-integers.
abs x	Absolute value (magnatude) of x
acos x	Arc cosine of x (in radians)
acosh x	Hyperbolic arc cosine of x (in radians)
asin x	Arc sine of x (in radians)
asinh x	Hyperbolic arc sine of x (in radians)
atan x	Arc tangent of x (in radians)
atanh x	Hyperbolic arc tangent of x (in radians)
ceil x	Ceiling of x — the smallest integer that’s >= x
cos x	Cosine of x (x is in radians)
cosh x	Hyperbolic cosine of x (x is in radians)
exp x	e^x (exponential/antilogarithm function with base e)
floor x	Floor of x — the largest integer that’s <= x
length x	String length of x
ln x	Natural logarithm of x
log x	Natural logarithm of x (synonym for ln, not base-10)
log10 x	Base-10 logarithm of x
not x	Logical NOT operator
round x	X, rounded to the nearest integer, using "gradeschool rounding"
sin x	Sine of x (x is in radians)
sinh x	Hyperbolic sine of x (x is in radians)
sqrt x	Square root of x. Result is NaN (Not a Number) if x is negative.
tan x	Tangent of x (x is in radians)
tanh x	Hyperbolic tangent of x (x is in radians)
trunc x	Integral part of a X, looks like floor(x) unless for negative number
random(n)	Get a random number in the range [0, n). If n is zero, or not provided, it defaults to 1.
fac(n)	n! (factorial of n: "n * (n-1) * (n-2) * … * 2 * 1") Deprecated. Use the ! operator instead.
min(a,b,…)	Get the smallest (minimum) number in the list
max(a,b,…)	Get the largest (maximum) number in the list
hypot(a,b)	Hypotenuse, i.e. the square root of the sum of squares of its arguments.
pyt(a, b)	Alias for hypot
pow(x, y)	Equivalent to x^y. For consistency with JavaScript's Math object.
atan2(y, x)	Arc tangent of x/y. i.e. the angle between (0, 0) and (x, y) in radians.
if(c, a, b)	Function form of c ? a : b
roundTo(x, n)	Rounds x to n places after the decimal point.