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index.js
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index.js
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// query buttons and screen
const numberButtons = document.querySelectorAll('.number-button');
const operatorButtons = document.querySelectorAll('.operator-button');
const evaluateButton = document.querySelector('#result-button');
const resetButton = document.querySelector('#reset-button');
const deleteButton = document.querySelector('#delete-button');
const equationScreen = document.querySelector('#equation-screen');
const resultScreen = document.querySelector('#result-screen');
// initial assignments
let firstOperand = '';
let secondOperand = '';
let operator = '';
let result= '';
function indexToAddSeparator(operand) {
const index = [operand.indexOf(','), operand.indexOf('.')].find(element => element !== -1) || operand.length;
if (index - 3 < 1) return -1;
return index;
}
function updateScreen(reset=false) {
if (reset) {
equation = '';
} else {
equation = `${firstOperand} ${operator} ${secondOperand}`;
}
equationScreen.textContent = equation;
resultScreen.textContent = result;
}
function reset() {
firstOperand = '';
secondOperand = '';
operator = '';
result = '';
updateScreen(true);
}
const containsDecimal = operand => operand.split('.').length == 2;
function assignOperands(numberCharacter) {
if (!operator) {
if (containsDecimal(firstOperand) && numberCharacter === '.') return;
firstOperand += numberCharacter;
} else {
if (containsDecimal(secondOperand) && numberCharacter === '.') return;
secondOperand += numberCharacter;
}
updateScreen();
}
function assignOperator(operatorCharacter) {
if (firstOperand && secondOperand && operator) evaluate();
if (firstOperand && !secondOperand) {
operator = operatorCharacter;
updateScreen();
}
return;
}
function evaluate() {
if (firstOperand && secondOperand && operator) {
firstOperand = Number(firstOperand);
secondOperand = Number(secondOperand);
switch(operator) {
case '+':
result = firstOperand + secondOperand;
break;
case '-':
result = firstOperand - secondOperand;
break;
case 'x':
result = firstOperand * secondOperand;
break;
case '/':
result = firstOperand / secondOperand;
break;
default:
break;
}
if (!Number.isInteger(result)) result = result.toFixed(2);
firstOperand = result;
secondOperand = '';
operator = '';
updateScreen();
}
}
function del() {
if (secondOperand) secondOperand = secondOperand.slice(0, -1);
else if (operator) operator = '';
else if (firstOperand) firstOperand = firstOperand.slice(0, -1);
else return;
if (secondOperand.endsWith('.')) secondOperand = secondOperand.slice(0, -1);
if (firstOperand.endsWith('.')) firstOperand = firstOperand.slice(0, -1);
updateScreen();
}
numberButtons.forEach(button => {
button.addEventListener('click', () => assignOperands(button.textContent));
});
operatorButtons.forEach(button => {
button.addEventListener('click', () => {
assignOperator(button.textContent);
evaluate();
});
});
resetButton.addEventListener('click', reset);
evaluateButton.addEventListener('click', () => {
if (firstOperand && secondOperand && operator) evaluate();
});
deleteButton.addEventListener('click', del);