JS简易计算器

简易计算器的制作,需获取输入框的id值以及value值,对按钮绑定点击事件.

    <input id="text1">
<select id="opt">
    <option value="请选择">请选择</option>
    <option value="+">+</option>
    <option value="-">-</option>
    <option value="*">*</option>
    <option value="/">/</option>
    <option value="%">%</option>
</select>
<input id="text2">
<button id="btn">=</button>
<input id="text3">

<script>
    function calc(n, m, str) {
        var res = 0;
        switch (str) {
            case "+":
                res = n + m;
                break;
            case "-":
                res = n - m;
                break;
            case "*":
                res = n * m;
                break;
            case "/":
                res = n / m;
                break;
            case "%":
                res = n % m;
                break;
            default:
                break;
        }

        return res;
    }



    var t1 = document.getElementById("text1");
    var opt = document.getElementById("opt");
    var t2 = document.getElementById("text2");
    var btn = document.getElementById("btn");
    var t3 = document.getElementById("text3");



    btn.onclick = function () {

        var strt1 = t1.value;
        var strt2 = t2.value;
        var strOpt = opt.value;

        if (strOpt == "请选择") {
            alert("请选择");
            return;
        }

        if (strt1 == "") {
            alert("请输入第一个数字");
            return;
        }

        if (strt2 == "") {
            alert("请输入第二个数字");
            return;
        }
        t3.value = calc(Number(strt1), Number(strt2),strOpt);
    }