diff --git a/01-js/hard/calculator.js b/01-js/hard/calculator.js
index 82d48229..0bf9cb69 100644
--- a/01-js/hard/calculator.js
+++ b/01-js/hard/calculator.js
@@ -1,22 +1,49 @@
-/*
-  Implement a class `Calculator` having below methods
-    - initialise a result variable in the constructor and keep updating it after every arithmetic operation
-    - add: takes a number and adds it to the result
-    - subtract: takes a number and subtracts it from the result
-    - multiply: takes a number and multiply it to the result
-    - divide: takes a number and divide it to the result
-    - clear: makes the `result` variable to 0
-    - getResult: returns the value of `result` variable
-    - calculate: takes a string expression which can take multi-arithmetic operations and give its result
-      example input: `10 +   2 *    (   6 - (4 + 1) / 2) + 7`
-      Points to Note: 
-        1. the input can have multiple continuous spaces, you're supposed to avoid them and parse the expression correctly
-        2. the input can have invalid non-numerical characters like `5 + abc`, you're supposed to throw error for such inputs
 
-  Once you've implemented the logic, test your code by running
-  - `npm run test-calculator`
-*/
+var math = require('mathjs');
+class Calculator {
+  constructor(){
+  this.result=0;
+  }
+ add(number){
+  this.result+=number
+}
+ subtract(number){
+  this.result-=number;
+}
+multiply(number){
+  this.result*=number;
+}
+divide(number){
+  if(number==0)
+  throw new Error("invalid number");
+  this.result/=number;
+}
+clear(){
+  this.result=0;
+} 
+getResult(){
+  return this.result; 
+}
+calculate(str){
+  var calculate =str.replace(/\s+/g,'');
+
+  if (/[^0-9+\-*/().\s]/.test(calculate)) {
+    throw new Error('non numeric characters in the expression');
+  }
+
+  const divisionByZeroPattern = /\/\s*0/g;
+var boolean = divisionByZeroPattern.test(calculate);
+if(boolean==true)
+throw new Error("division by 0 not allowed");
+  
+else{
+  this.result = math.evaluate(calculate); 
+    return this.result;
+  }
+}
+
+
+}
 
-class Calculator {}
 
 module.exports = Calculator;