app2.js

// Rewrite of JS functionality - Dom manipulation

// Basic storage variables and functions for calculator

const calculator = {
 memory: 0,
 storedFunction: "",
 screen: "",
 add(val) { this.memory += val; },
 subtract(val) { this.memory -= val; },
 times(val) { this.memory = this.memory * val; },
 divide(val) { this.memory = this.memory / val; },
}

// DOM Elements used:
const numberButtons = document.querySelectorAll(".number");
const functionButtons = document.querySelectorAll(".function");
const calcScreen = document.getElementById('entry');

// Write out function
const writeToScreen = () => {
 calcScreen.textContent = calculator.screen;
} 

// Adding functionality to number buttons
 // on click concat number to screen variable
 // write out to screen
numberButtons.forEach( (el) => {
 el.addEventListener('click', 
 () => {
 calculator.screen += el.textContent;
 writeToScreen();
 });
});

// Adding functionality to function keys
 // if clear button, clear all variables
 // if equals button, run memory number (1) with function and number on screen (2), store result in memory
 // else store number and function
functionButtons.forEach( (el) => {
 el.addEventListener('click', () => {
 if ( el.id == "clear" ) {
 calculator.memory = 0;
 calculator.storedFunction = ""; 
 calculator.screen = "";
 } else if ( el.id == "equals" ) {
 let method = calculator.storedFunction;
 calculator[method](parseInt(calculator.screen));
 calculator.screen = calculator.memory;
 } else {
 calculator.memory = parseInt(calculator.screen);
 calculator.storedFunction = el.id;
 calculator.screen = "";
 }
 writeToScreen();
 });
});

// Things to do:
 // add more buttons 
 // decimal point 
 // square button
 // Back button?
 // add compound calculations
 // more memory slots
 // add handler in print function for long inputs / rounding
 // add page embellishments
 // add keystroke option i.e typed input