JavaScript练习题

练习题

1.判断101-200之间有多少个素数，并输出所有素数

var tt=/^\d*$/;
        function ff() {
            let ss = "101到200之间的素数有:";
            for (let kk = 101; kk <= 200; kk++) {
                if (dd(kk)) {
                    ss += "<b>" + kk + "</b>,";
                }
            }
            if (ss.endsWith(","))
                ss = ss.substring(0, ss.length - 1);
            document.getElementById("div1").innerHTML = ss;
        }
        function dd(num) {
            let res = true;
            if(!tt.test(num))
                return false;
            for (let k = 2; k < num / 2; k++) {
                if (num % k == 0) {
                    res = false;
                    break;
                }
            }
            return res;
        }

2.求s=a+aa+aaa+aaaa+aa…a的值，其中a是一个数字。例如2+22+222+2222+22222(此时共有5个数相加)，几个数相加有键盘控制

   function ff() {
            let aa = document.getElementById("aa").value;
            let nn = document.getElementById("bb").value;
            aa = parseInt(aa);
            let res = dd(aa, nn);
            document.getElementById("span1").innerHTML = res;
        }
        function dd(aa, nn) {
            let res = 0;
            let bb = "";
            for (let k = 0; k < nn; k++) {
                bb += aa;
                let cc = parseInt(bb);
                res += cc;
            }
            return res;
        }

        function aa1() {
            let aa = document.getElementById("aa").value;
            let reg = /^[1-9]{1}$/;
            let ccc = reg.test(aa);
            if (!ccc) {
                document.getElementById("aaMsg").innerHTML = "输入数据不合法！";
            } else {
                document.getElementById("aaMsg").innerHTML = "";
            }
        }
        function bb1() {
            let aa = document.getElementById("bb").value;
            let reg = /^[1-9]\d*$/;
            let ccc = reg.test(aa);
            if (!ccc) {
                document.getElementById("bbMsg").innerHTML = "输入数据不合法！";
            } else {
                document.getElementById("bbMsg").innerHTML = "";
            }
        }

  <table>
        <tr>
            <td>a的值为:</td>
            <td><input id="aa" onblur="aa1()" maxlength="1" /><span class="error" id="aaMsg"></span></td>
        </tr>
        <tr>
            <td>次数：</td>
            <td><input id="bb" onblur="bb1()" /><span class="error" id="bbMsg"></span></td>
        </tr>
        <tr>
            <td>计算结果为：</td>
            <td><span id="span1"></span></td>
        </tr>
        <tr>
            <td colspan="2" align="center">
                <input type="button" onclick="ff()" value="计算" />
            </td>
        </tr>
    </table>

3.显示水仙花数

function ff(){
            for(let i=100;i<1000;i++){
                let ss="";
                i=i+"";
                a=i.charAt(1);
                b=i.charAt(2);
                c=i.charAt(3);
                i=parseInt(i);
                if(a*a*a+b*b*b+c*c*c==i){
                    ss+=i;
                }
            }
            document.getElementById("div1").innerHTML=ss;
        }

 <input type="button" value="显示水仙花数" onclick="ff()">
    <div id="div1"></div>

4.输入数据并判断

function ff(){
        let ss = document.getElementById("num1").value;
        let bb=false;
        let reg=/^\d*$/;
        bb=reg.test(ss);
        if(!bb){
            document.getElementById("error").innerHTML="<span class='error'>数据格式不正确！</span>"
        }else{
            let cc='';
            for(let k=0;k<ss.length;k++){
                cc+=ss.charAt(ss.length-1-k);
            }
            document.getElementById("error").innerHTML="输入数据为 " +cc;
        }
    }

    function dd(){
        document.getElementById("num1").value='';
        document.getElementById("error").innerHTML='';
    }

5.求质数

function ff(){            
            var ss=document.getElementById("num").value;
            let dd=/^\d*$/;
            let bb=dd.test(ss);
            if(bb){
                ss=parseInt(ss);
                bb=zhiShu(ss);
                if(bb){
                    document.getElementById("res").innerHTML=ss+"是质数";
                }else{
                    document.getElementById("res").innerHTML=ss+"不是质数";
                }
            }else{
                document.getElementById("res").innerHTML="<font color=red>输入数据不正确</font>";
            }
        }
        function zhiShu(num){
            let res=true;
            for(let k=2;k<num/2;k++){
                if(num%k==0){
                    res=false;
                    break;
                }
            }
            return res;
        }

6.点击自动显示对应菜单

 var aa = [{
            id: 1, title: '陕西省', children: [
                { id: 11, title: '西安市' }, { id: 12, title: '榆林市' }, { id: 13, title: '延安市' }
            ]
        }, {
            id: 2, title: '山西省', children: [
                { id: 21, title: '运城市' }, { id: 22, title: '临汾市' }
            ]
        }, {
            id: 3, title: '河南省', children: [
                { id: 31, title: '洛阳市' }
            ]
        }];
        function pp() {
            let sel = document.getElementById("prov").options;
            for (let k = 0; k < aa.length; k++) {
                let id = aa[k].id;
                let title = aa[k].title;
                let op = document.createElement("option");  //创建option元素对象，类似<option></option>
                op.value = id;  //设置option的提交值
                op.text = title; //设置option的显示值
                sel[sel.length] = op;  //将新创建的option加入到select的options数组中
            }
        }
        function ss(){
            let sel = document.getElementById("prov").value;
            let arr=[];
            for(let k=0;k<aa.length;k++){
                let id=aa[k].id;
                if(sel==id){
                    arr=aa[k].children;
                    break;
                }
            }
            let vv=document.getElementById("city").options;
            vv.length=1;  //将数组长度设置为1，则自动去除第一个元素之后的所有元素
            for(let k=0;k<arr.length;k++){
                let op=document.createElement("option");
                op.value=arr[k].id;
                op.text=arr[k].title;
                vv[vv.length]=op;
            }
        }

<select id="prov" onchange="ss()">
        <option value="">请选择省份</option>
    </select>
    <select id="city">
        <option value="">请选择城市</option>
    </select>