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함수가 함수를 반환하는 함수가 고차함수
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>계산기</title>
<style>
* { box-sizing: border-box;}
#result { width: 180px; height: 50px; margin: 5px; text-align: right;}
#operator { width: 50px; height: 50px; margin: 5px; text-align: center;}
button {width: 50px; height: 50px; margin: 5px;}
</style>
</head>
<body>
<input readonly id="operator">
<input readonly type="number" id="result">
<div class="row">
<button id="num-7">7</button>
<button id="num-8">8</button>
<button id="num-9">9</button>
<button id="plus">+</button>
</div>
<div class="row">
<button id="num-4">4</button>
<button id="num-5">5</button>
<button id="num-6">6</button>
<button id="minus">-</button>
</div>
<div class="row">
<button id="num-1">1</button>
<button id="num-2">2</button>
<button id="num-3">3</button>
<button id="divide">/</button>
</div>
<div class="row">
<button id="clear">C</button>
<button id="num-0">0</button>
<button id="calculate">=</button>
<button id="multiply">x</button>
</div>
<script>
let numOne = '';
let operator = '';
let numTwo = '';
const $operator = document.querySelector('#operator');
const $result = document.querySelector('#result');
const onClickNumber = (event) => { // 함수가 함수를 리턴한다
if (operator) { // 비어있지 않다
if (!numTwo) {
$result.value = '';
}
numTwo += event.target.textContent; // 내가 클릭한 타겟의 글자를 가져온다
} else { // 비어있다
numOne += event.target.textContent;
}
$result.value += event.target.textContent;
}
document.querySelector('#num-0').addEventListener('click', onClickNumber);
document.querySelector('#num-1').addEventListener('click', onClickNumber);
document.querySelector('#num-2').addEventListener('click', onClickNumber);
document.querySelector('#num-3').addEventListener('click', onClickNumber);
document.querySelector('#num-4').addEventListener('click', onClickNumber);
document.querySelector('#num-5').addEventListener('click', onClickNumber);
document.querySelector('#num-6').addEventListener('click', onClickNumber);
document.querySelector('#num-7').addEventListener('click', onClickNumber);
document.querySelector('#num-8').addEventListener('click', onClickNumber);
document.querySelector('#num-9').addEventListener('click', onClickNumber);
// 고차함수 사용
const onClickOperator = (op) => () => {
if(numTwo) {
switch (operator) {
case '+':
$result.value = parseInt(numOne) + parseInt(numTwo);
break;
case '-':
$result.value = numOne - numTwo;
break;
case '/':
$result.value = numOne / numTwo;
break;
case '*':
$result.value = numOne * numTwo;
break;
default:
break;
}
numOne = $result.value;
numTwo = '';
}
if(numOne) {
operator = op;
$operator.value = op;
} else {
alert('숫자를 먼저 입력하세요.');
}
}
document.querySelector('#plus').addEventListener('click', onClickOperator('+'));
document.querySelector('#minus').addEventListener('click', onClickOperator('-'));
document.querySelector('#divide').addEventListener('click', onClickOperator('/'));
document.querySelector('#multiply').addEventListener('click', onClickOperator('*'));
document.querySelector('#calculate').addEventListener('click', () => {
if (numTwo) {
switch (operator) {
case '+':
$result.value = parseInt(numOne) + parseInt(numTwo);
break;
case '-':
$result.value = numOne - numTwo;
break;
case '/':
$result.value = numOne / numTwo;
break;
case '*':
$result.value = numOne * numTwo;
break;
default:
break;
}
}
// [=] 버튼을 클릭 했을 때
// 1. 연산자를 없애준다.
$operator.value = '';
// 2. 첫 번째 숫자에 계산된 결과 값을 넣는다.
numOne = $result.value;
// 3. 초기화 한다.
operator = '';
numTwo = '';
});
document.querySelector('#clear').addEventListener('click', () => {
numOne = '';
operator = '';
numTwo = '';
$operator.value = '';
$result.value = '';
});
</script>
</body>
</html>
JavaScript
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