calculator.js

let runningTotal = 0;
let buffer = "0";
let previousOperator = null;
const screen = document.querySelector('.screen');

document.querySelector('.calc-buttons').addEventListener("click", function(event){
    buttonClick(event.target.innerText);   
})

function buttonClick(value){
    if (isNaN(parseInt(value))) {
        handleSymbol(value);

    } else {
        handleNumber(value)  
    }
    rerender();
}
function handleNumber (value){
 if (buffer === "0"){
     buffer = value;
 } else {
     buffer += value;
 }
 rerender ();
}
function handleSymbol(value){
    switch (value) {
        case 'C' :
        buffer = "0";
        runningTotal = 0;
        previousOperator = null;
        break;
    case '=':
        if (previousOperator === null) {
            return;
        }
        flushOperation (parseInt(buffer));
        previousOperator = null;
        buffer = "" + runningTotal;
        runningTotal = 0
        break;
        case "->":
        if (buffer.length === 1){
            buffer = "0";
        } else {
            buffer = buffer.substring(0, buffer.length -1);
            }
                break;
        default:
        handlemath(value);
        break;  
    }
}
function handlemath(value){
    const intBuffer = parseInt(buffer);
    if (runningTotal === 0){
        runningTotal = intBuffer;
    } else {flushOperation(intBuffer)
    }previousOperator = value;
 buffer = "0";
}
function flushOperation(intBuffer)
{
    if (previousOperator === '+') {
        runningTotal += intBuffer
    } else if (previousOperator === '-') {
        runningTotal -= intBuffer
    } else if (previousOperator === 'X') {
        runningTotal *= intBuffer
    } else {
        runningTotal /= intBuffer
    }
        
    }


function rerender (){
    screen.innerText = buffer;
}