script.js

window.onload = function() {
    function getHistory() {
        return document.getElementById("history-value").innerText;
        
    }
    function printHistory(num) {
        document.getElementById("history-value").innerText=num;
    }

    function getOutput() {
        return document.getElementById("output-value").innerText;
        
    }
    function printOutput(num) {
        if (num==""){
            document.getElementById("output-value").innerText=num;
        } else {
            document.getElementById("output-value").innerText=getFormattedNumber(num);
        }
        
      
    }

    function getFormattedNumber(num) {
        if (num=="-") {
            return "";
        }
        var n = Number(num);
        var value = n.toLocaleString("en");
        return value;

    }


    function reverseNumberFormat(num) {
        return Number(num.replace(/,/g,''));
    }
    
    var operator = document.getElementsByClassName("operator");
    for (var i=0; i<operator.length;i++) {
        operator[i].addEventListener('click', function(){
            if(this.id=="clear"){
                printHistory("");
                printOutput("");
            }
            else if (this.id=="backspace"){
                var output = reverseNumberFormat(getOutput()).toString();
                if(output) {
                    output = output.substr(0,output.length-1);
                    printOutput(output);
                }
            } else {
                var output=getOutput();
                var history=getHistory();
                if (output==""&&history!="") {
                if (isNaN(history[history.length-1])) 
                history = history.substr(0,history.length-1);
                }
                if (output!=="" || history!="") {
                    output= output==""?
                    output:reverseNumberFormat(output);
                    history=history+output;
                    if(this.id=="=") {
                        var result = eval(history);
                        printOutput(result);
                        printHistory("");
                    } else {
                        history = history+this.id;
                        printHistory(history);
                        printOutput("");
                    }
                }
            }
        })
    }

   var number = document.getElementsByClassName("number");
   for(var i=0;i<number.length;i++){
       number[i].addEventListener('click', function(){
           var output = reverseNumberFormat(getOutput());
           if(output!=NaN) {
               output=output+this.id;
               printOutput(output);
           }
       })
   }
  








































}