Peg it !

/*
 * Classic example grammar, which recognizes simple arithmetic expressions like
 * "2*(3+4)". The parser generated from this grammar then computes their value.
 */

start
  = additive

additive
  = left:multiplicative tail:(additive_op multiplicative)* { return tail.reduce(function(n,t){return t[0](n,t[1])},left); }
  / multiplicative

multiplicative
  = left:primary "*" right:multiplicative { return left * right; }
  / primary

primary
  = integer
  / "(" additive:additive ")" { return additive; }

integer "integer"
  = digits:[0-9]+ { return parseInt(digits.join(""), 10); }

additive_op
  = "+" { return function(a,b){return a+b;}; }
  / "-" { return function(a,b){return a-b;}; }