Get around floating point precision of JavaScript fixes #5

Fix `equation` not working on parentheses wrapped variables
Fixed `parseExpression` not working correctly on nested function operators

lib/index.js

@@ -49,7 +49,11 @@ let Equation = {
     let stack = parseExpression(expression);
     let variables = [];
 
-    stack.forEach(a => {
+    stack.forEach(function varCheck(a) {
+      if (Array.isArray(a)) {
+        return a.forEach(varCheck);
+      }
+
       if (typeof a === 'string' && !_.isNumber(a) &&
           !operators[a] && a === a.toLowerCase()) {
         // grouped variables like (y) need to have their parantheses removed
@@ -125,23 +129,32 @@ const parseExpression = expression => {
     }
 
     // it's probably a function with a length more than one
-    if (!_.isNumber(cur) && !operators[cur] && cur !== '.') {
+    if (!_.isNumber(cur) && !operators[cur] && cur !== '.' &&
+        cur !== '(' && cur !== ')') {
+
       record += cur;
     } else if (record.length) {
       stack.push(record, cur);
       record = '';
-    } else if (_.isNumber(stack[stack.length - 1]) &&
+    } else if (_.isNumber(stack[past]) &&
               (_.isNumber(cur) || cur === '.')) {
 
-      stack[stack.length - 1] += cur;
-    } else if (stack[past] === '-') {
-      const beforeSign = stack[stack.length - 2];
+      stack[past] += cur;
 
+      // negation sign
+    } else if (stack[past] === '-') {
+      const beforeSign = stack[past - 1];
+
+      // 2 / -5 is OK, pass
       if (operators[beforeSign]) {
         stack[past] += cur;
+
+        // (2+1) - 5 becomes (2+1) + -5
       } else if (beforeSign === ')') {
         stack[past] = '+';
         stack.push(`-${cur}`);
+
+        // 2 - 5 is also OK, pass
       } else if (_.isNumber(beforeSign)) {
         stack.push(cur);
       } else {
@@ -272,12 +285,13 @@ const evaluate = stack => {
   if (!op) {
     return stack[0];
   }
+
   const { left } = formatInfo(op);
 
   let leftArguments = stack.slice(0, left),
       rightArguments = stack.slice(left + 1);
 
-  return operators[op].fn(...leftArguments, ...rightArguments);
+  return fixFloat(operators[op].fn(...leftArguments, ...rightArguments));
 };
 
 /**
@@ -315,4 +329,16 @@ const replaceConstants = expression => {
   });
 };
 
+/**
+  * Fixes JavaScript's floating point precisions - Issue #5
+  *
+  * @param {Number} number
+  *        The number to fix
+  * @return {Number}
+  *         Fixed number
+  */
+const fixFloat = number => {
+  return +number.toFixed(15);
+};
+
 export default Equation;

lib/operators.js

@@ -88,5 +88,15 @@ export default {
     fn: Math.cot,
     format: '10',
     precedence: -1
+  },
+  'round': {
+    fn: Math.round,
+    format: '10',
+    precedence: -1
+  },
+  'floor': {
+    fn: Math.floor,
+    format: '10',
+    precedence: -1
   }
 };