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script.js
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script.js
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// Initializing data structures for storing data
let buffer = [];
let currentlyHeldOperator = null;
let inputsForDisplay = [];
let reversePolishNotation = [];
// Constants
const NUMBERS = ["0", "1", "2", "3", '4', '5', "6", "7", "8", "9"];
const OPERATORS = ["+", "-", "*", "/"];
const DECIMAL_ACCURACY = 6;
const INITIAL_RESULT_DISPLAY_VALUE = "";
const DIVIDE_BY_ZERO_ERROR = "DIVIDEBYZERO"
const DIVIDE_BY_ZERO_MESSAGE = "STOP DIVIDING BY ZERO"
const SYNTAX_ERROR_MESSAGE = "SYNTAX ERROR, HIT CLEAR"
const MISSING_NUMBERS_MESSAGE = "Forgetting some numbers?"
const FINISHED_CALCULATION = "finished"
function add(a, b) {
return Number(a) + Number(b);
}
function subtract(a, b) {
return Number(a) - Number(b);
}
function multiply(a, b) {
return Number(a) * Number(b);
}
function divide(a, b) {
if (b === "0") {
return DIVIDE_BY_ZERO_ERROR
}
// In order to round to a given decimal accuracy
// Number.Epsilon is to ensure correct rounding per https://stackoverflow.com/questions/11832914/how-to-round-to-at-most-2-decimal-places-if-necessary
return Math.round((Number(a)/Number(b) + Number.EPSILON) * 10**DECIMAL_ACCURACY)/(10**DECIMAL_ACCURACY);
}
function operate(symbol, a, b) {
switch (symbol) {
case "+":
return add(a,b);
case "-":
return subtract(a,b);
case "*":
return multiply(a,b);
case "/":
return divide(a,b);
}
}
function calculateFromReversePolishNotation(rpn) {
let runningResult = 0;
const workingRPN = [...rpn]
while (workingRPN.length > 1) {
const [num1, num2, mathSymbol] = workingRPN.splice(0,3)
runningResult = operate(mathSymbol, num1, num2)
if (runningResult === DIVIDE_BY_ZERO_ERROR) {
return DIVIDE_BY_ZERO_MESSAGE
}
workingRPN.unshift(runningResult)
}
return runningResult;
}
function updateInputDisplay(list) {
const displayScreen = document.querySelector(`.input`);
displayScreen.textContent = list.join("");
}
function addToInputDisplay(character, list) {
list.push(character);
updateInputDisplay(list);
}
function updateResultDisplay(value) {
const displayScreen = document.querySelector(`.results`);
displayScreen.textContent = value;
}
function clearAll() {
buffer = [];
currentlyHeldOperator = null;
inputsForDisplay = [];
reversePolishNotation = [];
updateInputDisplay([])
updateResultDisplay(INITIAL_RESULT_DISPLAY_VALUE)
}
function doesArrayContainOperator(array) {
return array.some( (element) => OPERATORS.includes(element));
}
function doesArrayContainNumber(array) {
return array.some( (element) => NUMBERS.includes(element));
}
// After calculation is done, clicking on another button will clear the previous information and also the display
const buttons = document.querySelectorAll("button");
buttons.forEach( (button) => {
button.addEventListener("click", (e) => {
if (currentlyHeldOperator === FINISHED_CALCULATION) {
clearAll()
}
})
})
const clearButton = document.querySelector("#clear");
clearButton.addEventListener("click", (e) => {
clearAll();
})
const digitButtons = document.querySelectorAll(".digit");
digitButtons.forEach( (digitButton) => {
digitButton.addEventListener("click", (e) => {
const digit = e.target.getAttribute("data-value")
// If a digit button is clicked after an Operator button, start a new number in buffer
if (doesArrayContainOperator(buffer)) {
buffer = [digit]
addToInputDisplay(digit, inputsForDisplay);
} else if (buffer.length == 0 || doesArrayContainNumber(buffer)) {
buffer.push(digit);
addToInputDisplay(digit, inputsForDisplay);
}
})
})
const operatorButtons = document.querySelectorAll(".operator");
operatorButtons.forEach( (operatorButton) => {
operatorButton.addEventListener("click", (e) => {
const symbol = e.target.getAttribute("data-value")
if (buffer.length === 0) {
// If no numbers were chosen before hitting operator button, display syntax error
clearAll();
updateResultDisplay(SYNTAX_ERROR_MESSAGE);
return;
}
if (doesArrayContainOperator(buffer)) {
// If "characters" includes an operator, update chosen operator
buffer = [symbol];
currentlyHeldOperator = symbol;
inputsForDisplay.splice(-1,1,` ${symbol} `);
updateInputDisplay(inputsForDisplay);
return;
}
if (currentlyHeldOperator) {
// For the nth operator selection (when there is an operator in the currentlyHeldOperator)
reversePolishNotation.push(buffer.join(""), currentlyHeldOperator);
buffer = [symbol];
currentlyHeldOperator = symbol;
addToInputDisplay(` ${symbol} `, inputsForDisplay);
return;
}
if (!currentlyHeldOperator) {
// The first operator selection (aka when currentlyHeldOperator = null)
reversePolishNotation.push(buffer.join(""));
buffer = [symbol];
currentlyHeldOperator = symbol;
addToInputDisplay(` ${symbol} `, inputsForDisplay);
return;
}
})
})
const equalButton = document.querySelector(".equal");
equalButton.addEventListener("click", (e) => {
if (doesArrayContainOperator(buffer)) {
updateResultDisplay(MISSING_NUMBERS_MESSAGE)
return
}
reversePolishNotation.push(buffer.join(""), currentlyHeldOperator);
// Signals that calculation is finished so next keystroke after "=" starts new calculation
currentlyHeldOperator = FINISHED_CALCULATION;
const output = calculateFromReversePolishNotation(reversePolishNotation)
updateResultDisplay(output)
})
// Initializes calculator result display
document.querySelector(`.results`).textContent = INITIAL_RESULT_DISPLAY_VALUE