npm install sheva

var parser = require("sheva")();

(function(){
	var And      = parser.And.bind(parser)
	var Or       = parser.Or.bind(parser)
	var MoreThan = parser.MoreThan.bind(parser)
	var Optional = parser.Optional.bind(parser)
	var Is       = parser.Is.bind(parser)
	var Digit    = parser.Digit.bind(parser)
	var $        = parser.$.bind(parser)
	
  parser.token({
    "LB"    : Is("("),
    "RB"    : Is(")"),
    "PLUS"  : Is("+"),
    "MINUS" : Is("-"),
    "MUL"   : Is("*"),
    "DIV"   : Is("/"),
    "NUM"   : (function () {
      var digits = MoreThan(0, Digit)
      var sign = Or(Is("-"), Is("+"))
      var dot = Is(".")
      return And(Optional(sign), digits, Optional(And(dot, digits)))
    })()
  })

  parser.grammar({
    "Expr"     : And($("Term"), Optional(MoreThan(0, $("MoreExpr")))),
    "MoreExpr" : And($("TermOp"), $("Term")),
    "Term"     : And($("Factor"), Optional(MoreThan(0, $("MoreTerm")))),
    "MoreTerm" : And($("FactorOp"), $("Factor")),
    "TermOp"   : Or(Is("PLUS"), Is("MINUS")),
    "Factor"   : Or($("P-Expr"), Is("NUM")),
    "P-Expr"   : And(Is("LB"), $("Expr"), Is("RB")),
    "FactorOp" : Or(Is("MUL"), Is("DIV"))
  })

  parser.action({
    "NUM"      : function (n) { n.extra = parseFloat(n.value) },
    "Factor"   : function (n) { n.extra = n.children[0].extra },
    "MoreTerm" : function (n) { n.extra = n.children[1].extra },
    "MoreExpr" : function (n) { n.extra = n.children[1].extra },
    "P-Expr"   : function (n) { n.extra = n.children[1].extra },
    "Term"     : function (n) {
      n.extra = n.children[0].extra
      var child = n.children[1]
      for (var i = 0; child && i < child.children.length; i+=2) {
        var FactorOp = child.children[i]
        var Factor = child.children[i+1]

        switch (FactorOp.value) {
          case "*": n.extra *= Factor.extra;break;
          case "/": n.extra /= Factor.extra;break;
        }
      }
    },
    "Expr"    : function (n) {
      n.extra = n.children[0].extra
      var child = n.children[1]
      for (var i = 0; child && i < child.children.length; i+=2) {
        var TermOp = child.children[i]
        var Term = child.children[i+1]

        switch (TermOp.value) {
          case "+": n.extra += Term.extra;break;
          case "-": n.extra -= Term.extra;break;
        }
      }
    },
  })
    
  console.log(parser.parse("Expr", "(1+2)*(3+4+5)"))
})()