jscript1.js

var input=document.getElementById('input'),
number= document.querySelectorAll('.numbers div'),
operator = document.querySelectorAll('.operators div'),
result = document.getElementById('result'),
clear= document.getElementById('clear'),

resultDisplayed = false;

for (var i = 0; i < number.length; i++) {
    number[i].addEventListener("click",function(e){
        var currentString = input.innerHTML;
        var lastChar = currentString [currentString.length-1];
        
        
        if (resultDisplayed === false) {
            input.innerHTML +=e.target.innerHTML;
            
            
        }
        else if( resultDisplayed=== true && lastChar === "+" || lastChar === "-" || lastChar === "×" || lastChar === "÷"){
            resultDisplayed = false;
            input.innerHTML += e.target.innerHTML;
        }
        else{
            resultDisplayed = false;
            input.innerHTML="";
            input.innerHTML += e.target.innerHTML;
        }

    });
    
}
for (var i = 0; i < operator.length; i++) {
     operator[i].addEventListener("click",function(e){
         var currentString = input.innerHTML;
         var lastChar = currentString[currentString.length-1];
         if(lastChar === "+" || lastChar === "-" || lastChar === "×" || lastChar === "÷"){
             var newString =currentString.substring(0,currentString.length-1)+ e.target.innerHTML;
             input.innerHTML = newString;

         }
         else if(currentString.length == 0){
             console.log("enter a number first");

         }
         else{
             input.innerHTML += e.target.innerHTML;
         }
        
     });
    
}
result.addEventListener("click", function(){
    var inputString=input.innerHTML;
    var numbers = inputString.split(/\+|\-|\×|\÷/g);

    var operators = inputString.replace(/[0-9]|\./g, "").split("");
    console.log(inputString);
    console.log(operators);
    console.log(numbers);
    console.log("  _ _ _ _ _")
    var divide = operators.indexOf("÷");
    while (divide != -1) {
        numbers.splice(divide,2,numbers[divide]/numbers[divide+1]);
        operators.splice(divide,1);
        divide = operators.indexOf("÷");
        
    }
    var multiply = operators.indexOf("×");
    while (multiply != -1) {
        numbers.splice(multiply,2,numbers[multiply] * numbers[multiply+1]);
        operators.splice(multiply,1);
        multiply=operators.indexOf("×");
        
    }
    var subtract = operators.indexOf("-");
    while (subtract != -1) {
        numbers.splice(subtract,2,numbers[subtract]- numbers[subtract+1]);
        operators.splice(subtract,1);
        subtract=operators.indexOf("-");
        
    }
    var add = operators.indexOf("+");
    while (add != -1) {
        numbers.splice(add,2,parseFloat (numbers[add])+ parseFloat (numbers[add+1]));
        operators.splice(add,1);
        add=operators.indexOf("+");
        
    }
    input.innerHTML = numbers[0];
    resultDisplayed = true;
});
clear.addEventListener("click",function(){
    input.innerHTML = "";
})