popup.js

document.getElementById("submit").addEventListener("click", calculate)
document.getElementById("7b").addEventListener("click", () => (des(7)))
document.getElementById("8b").addEventListener("click", () => (des(8)))
document.getElementById("9b").addEventListener("click", () => (des(9)))
document.getElementById("4b").addEventListener("click", () => (des(4)))
document.getElementById("5b").addEventListener("click", () => (des(5)))
document.getElementById("6b").addEventListener("click", () => (des(6)))
document.getElementById("1b").addEventListener("click", () => (des(1)))
document.getElementById("2b").addEventListener("click", () => (des(2)))
document.getElementById("3b").addEventListener("click", () => (des(3)))
document.getElementById("0b").addEventListener("click", () => (des(0)))
document.getElementById("+b").addEventListener("click", () => (des("+")))
document.getElementById("/b").addEventListener("click", () => (des("/")))
document.getElementById("-b").addEventListener("click", () => (des("-")))
document.getElementById("*b").addEventListener("click", () => (des("*")))

function calculate(){
    var input = document.getElementById("textField").value
    const value = eval(input)
    document.getElementById("textField").value=value
}

function des(val){

    document.getElementById("textField").value+=val
}