Javascript Math.cos and Math.sin are inaccurate. Is there any solution?

It's very, very close to zero, though. (~ 10^-16)

And alert(Math.sin(Math.PI/2)) does return 1.

It's just one of things you have to be careful of when dealing with floating point arithmetic. Rounding errors pop up all over the place.

you can use

Math.sin(Math.PI).toFixed(3) // "0.000"

Examples:

const cos = (a) => Math.cos(Math.PI * a / 180); cos(90) // 6.123233995736766e-17

then you can use .toFixed()

cos(90).toFixed(3) // "0.000"

.toFixed() returns string, so you can parse it to float using parseFloat()

parseFloat(cos(90).toFixed(3)) // 0.000