Install with Bower:
$ bower install evaluatex
Node package coming soon. Get zipped releases here. Check it on Github.
Evaluatex parses ASCII and LaTeX math quickly and safely. Punch in an expression into a textbox and watch as Evaluatex does the heavy math work so you don't have to! It's especially powerful when combined with math markup tools such as Mathquill.
You can use all of the constants defined in Javascript's Math object, such as sin() and PI.
Hit up the README to see the whole feature-set.