JavaScript实现简单计算器
适合初学者参考的简易计算器，里面没有太多的难以理解的方法，使用的是最基础的JS语法解决式子的运算问题，同时处理了式子中的运算优先级。
实现思路
1、通过绑定点击事件实现待计算式子的输入
2、遍历原式子，读取式子中乘除运算符的位置
3、优先处理乘除取余运算
4、处理加减运算
5、返回结果
代码：
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta http-equiv="X-UA-Compatible" content="ie=edge">
<title>Document</title>
</head>
<body>
<!-- 计算器 -->
<style>
.work2{
width: 500px;
margin-top: 50px;
}
h2{
color: #333;
}
#work2Article1{
width: 100%;
height: 200px;
background: #cccccc;
font-size: 20px;
}
#work2Article2{
width: 100%;
height: 400px;
background: #cccccc;
}
#work2Article2 button{
width: 24.1%;
height: 20%;
color: #333;
background: #999;
}
.work2 button{
font-size: 20px;
}
</style>
<section class="work2">
<h2>计算器</h2>
<article id="work2Article1">
</article>
<article id="work2Article2">
<button id="work2BtnCle">AC</button>
<button id="work2BtnDel">×</button>
<button id="work2BtnRem">%</button>
<button id="work2BtnDiv">/</button>
<button id="work2Btn7">7</button>
<button id="work2Btn8">8</button>
<button id="work2Btn9">9</button>
<button id="work2BtnMul">*</button>
<button id="work2Btn4">4</button>
<button id="work2Btn5">5</button>
<button id="work2Btn6">6</button>
<button id="work2BtnSub">-</button>
<button id="work2Btn1">1</button>
<button id="work2Btn2">2</button>
<button id="work2Btn3">3</button>
<button id="work2BtnAdd">+</button>
<button id="work2BtnNull">未开发</button>
<button id="work2Btn0">0</button>
<button id="work2BtnPoi">.</button>
<button id="work2BtnEqu">=</button>
</article>
</section>
<script>
var num = "0"; //输入的原式
var res = 0 ; //结果
var work2Article1 = document.getElementById('work2Article1');
var work2BtnCle = document.getElementById('work2BtnCle');
var work2BtnDiv = document.getElementById('work2BtnDiv');
var work2BtnDel = document.getElementById('work2BtnDel');
var work2BtnRem = document.getElementById('work2BtnRem');
var work2BtnMul = document.getElementById('work2BtnMul');
var work2BtnSub = document.getElementById('work2BtnSub');
var work2BtnAdd = document.getElementById('work2BtnAdd');
var work2BtnNull = document.getElementById('work2BtnNull');
var work2BtnPoi = document.getElementById('work2BtnPoi');
var work2BtnEqu = document.getElementById('work2BtnEqu');
var work2Btn1 = document.getElementById('work2Btn1');
var work2Btn2 = document.getElementById('work2Btn2');
var work2Btn3 = document.getElementById('work2Btn3');
var work2Btn4 = document.getElementById('work2Btn4');
var work2Btn5 = document.getElementById('work2Btn5');
var work2Btn6 = document.getElementById('work2Btn6');
var work2Btn7 = document.getElementById('work2Btn7');
var work2Btn8 = document.getElementById('work2Btn8');
var work2Btn9 = document.getElementById('work2Btn9');
var work2Btn0 = document.getElementById('work2Btn0');
// 初始化
work2BtnCle.onclick = function () {
num = "0" ;
work2Article1.innerText=`${num}`;
}
work2BtnDel.onclick = function () {
// 判断原式长度，长度为1时变为0
if(num.length==1){
num = '0' ;
work2Article1.innerText=num;
// 否则减去最后一位
}else{
num = num.substring(0,num.length-1);
work2Article1.innerText=num;
}
}
// 运算符点击事件
work2BtnDiv.onclick = function () {
num += "/"
work2Article1.innerText=num;
}
work2BtnRem.onclick = function () {
num += "%" ;
work2Article1.innerText=`${num}`;
}
work2BtnMul.onclick = function () {
num += "*" ;
work2Article1.innerText=`${num}`;
}
work2BtnAdd.onclick = function () {
num += "+" ;
work2Article1.innerText=`${num}`;
}
work2BtnNull.onclick = function () {
alert('下次一定开发出来');
}
work2BtnPoi.onclick = function () {
num += "." ;
work2Article1.innerText=`${num}`;
}
work2BtnSub.onclick = function () {
num += "-" ;
work2Article1.innerText=`${num}`;
}
// 数字点击事件
work2Btn1.onclick =function(){
if( num == "0" ){
num = "1";
}else{
num += "1" ;
}
work2Article1.innerText=`${num}`;
}
work2Btn2.onclick =function(){
if( num == "0" ){
num = "2";
}else{
num += "2" ;
}
work2Article1.innerText=`${num}`;
}
work2Btn3.onclick =function(){
if( num == "0" ){
num = "3";
}else{
num += "3" ;
}
work2Article1.innerText=`${num}`;
}
work2Btn4.onclick =function(){
if( num == "0" ){
num = "4";
}else{
num += "4" ;
}
work2Article1.innerText=`${num}`;
}
work2Btn5.onclick =function(){
if( num == "0" ){
num = "5";
}else{
num += "5" ;
}
work2Article1.innerText=`${num}`;
}
work2Btn6.onclick =function(){
if( num == "0" ){
num = "6";
}else{
num += "6" ;
}
work2Article1.innerText=`${num}`;
}
work2Btn7.onclick =function(){
if( num == "0" ){
num = "7";
}else{
num += "7" ;
}
work2Article1.innerText=`${num}`;
}
work2Btn8.onclick =function(){
if( num == "0" ){
num = "8";
}else{
num += "8" ;
}
work2Article1.innerText=`${num}`;
}
work2Btn9.onclick =function(){
if( num == "0" ){
num = "9";
}else{
num += "9" ;
}
work2Article1.innerText=`${num}`;
}
work2Btn0.onclick =function(){
if( num == "0" ){
num = "0";
}else{
num += "0" ;
}
work2Article1.innerText=`${num}`;
}
work2BtnEqu.onclick = function () {
// num = Number(num);
//检测运算符号的位置
function obtainSymbol(){
var num1 = [];
var o = 0 ;
for(var i = 0 ; i<=num.length ; i++){
if(num.charAt(i)=='+'){
num1[o] = i ;
o++;
}else if(num.charAt(i)=='-'){
num1[o] = i ;
o++;
}else if(num.charAt(i)=='*'){
num1[o] = i ;
o++;
}else if(num.charAt(i)=='/'){
num1[o] = i ;
o++;
}else if(num.charAt(i)=='%'){
num1[o] = i ;
o++;
}
}
return num1 ;
}
var res1 = 0 ; //计算结果
var numStar = num ; //重新获取原式子
// 检测乘除取余运算
var num1 = obtainSymbol();
console.log(num1);
// 检测除了第一个符号之外的乘除取余运算
for( var w = 0 ; w <= num1.length ; w++ ){
if(w != 0){
if( num.charAt(num1[w]) == '*' || num.charAt(num1[w]) == '/' || num.charAt(num1[w]) == '%' ){
if(w != num1.length-1){
switch(num.charAt(num1[w])){
case '*': var l =Number(num.substring(num1[w-1],num1[w]))*Number(num.substring(num1[w]+1,num1[w+1])) ;
console.log(l);
num = num.substring(0,num1[w-1]+1) + l + num.substring(num1[w+1]) ;
break;
case '/': var l =Number(num.substring(num1[w-1],num1[w]))*Number(num.substring(num1[w]+1,num1[w+1])) ;
num = num.substring(0,num1[w-1]+1) + l + num.substring(num1[w+1]) ; break;
case '%': var l =Number(num.substring(num1[w-1],num1[w]))*Number(num.substring(num1[w]+1,num1[w+1])) ;
num = num.substring(0,num1[w-1]+1) + l + num.substring(num1[w+1]) ; break;
}
}else if(w == num1.length-1 ){
switch(num.charAt(num1[w])){
case '*': var l =Number(num.substring(num1[w-1]+1,num1[w])) * Number(num.substring(num1[w]+1)) ;
num = num.substring(0,num1[w-1]+1) + l ;
break;
case '/': var l =Number(num.substring(num1[w-1]+1,num1[w])) / Number(num.substring(num1[w]+1)) ;
num = num.substring(0,num1[w-1]+1) + l ; break;
case '%': var l =Number(num.substring(num1[w-1]+1,num1[w])) % Number(num.substring(num1[w]+1)) ;
num = num.substring(0,num1[w-1]+1) + l; break;
}
}
num1 = 0 ;
num1 = obtainSymbol();
w -= 1;
}
}
}
// 从第一位运算符开始运算
for(var k = 0 ; k < num1.length ; k++){
if(k==0){
switch(num.charAt(num1[k])){
case '+': res1 += Number(num.substring(0,num1[k])) + Number(num.substring(num1[k]+1,num1[k+1])) ; break;
case '-': res1 += Number(num.substring(0,num1[k])) - Number(num.substring(num1[k]+1,num1[k+1])) ; break;
case '*': res1 += Number(num.substring(0,num1[k])) * Number(num.substring(num1[k]+1,num1[k+1])) ; break;
case '/': res1 += Number(num.substring(0,num1[k])) / Number(num.substring(num1[k]+1,num1[k+1])) ; break;
case '%': res1 += Number(num.substring(0,num1[k])) % Number(num.substring(num1[k]+1,num1[k+1])) ; break;
}
}else{
switch(num.charAt(num1[k])){
case '+':
if(k==num1.length-1){
res1 += Number(num.substring(num1[k]+1)) ;
}else{
res1 += Number(num.substring(num1[k]+1,num1[k+1]));
}break;
case '-':
if(k==num1.length-1){
res1 -= Number(num.substring(num1[k]+1)) ;
}else{
res1 -= Number(num.substring(num1[k]+1,num1[k+1]));
}break;
case '*':
if(k==num1.length-1){
res1 *= Number(num.substring(num1[k]+1)) ;
}else{
res1 *= Number(num.substring(num1[k]+1,num1[k+1]));
}break;
case '/':
if(k==num1.length-1){
res1 /= Number(num.substring(num1[k]+1)) ;
}else{
res1 /= Number(num.substring(num1[k]+1,num1[k+1]));
}break;
case '%':
if(k==num1.length-1){
res1 %= Number(num.substring(num1[k]+1)) ;
}else{
res1 %= Number(num.substring(num1[k]+1,num1[k+1]));
}break;
}
}
}
work2Article1.innerText=`${numStar}=${res1}`;
}
</script>
</body>
</html>
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