简易计算器实现退格删除！求帮助

_MAYAWEN 2018-07-11 11:44:08

前端新手，学习js后自己做了一个简易计算器，怎么都实现不了退格删除一个数字；我的想法是得到输入的数字然后value.length-1；请大家帮我看看代码！谢谢
<script>
/* display result */
function get(value) {
document.getElementById("display").value += value;
}

/* delete */
function del(value) {
document.getElementById("display").value = "";
}

/* calcula */
function calculates() {
var result = 0;
result = document.getElementById("display").value;
document.getElementById("display").value = "";
document.getElementById("display").value = eval(result);
}
</script>

</head>

<body>
<div class="center">
<h1>计算器</h1>
<form name="calculator">
<input type="text" id="display">
<input type="button" class="btn other" value="C" onclick="del(this.value)">
<br>
<input type="button" class="btn number" value="7" onclick="get(this.value);">
<input type="button" class="btn number" value="8" onclick="get(this.value);">
<input type="button" class="btn number" value="9" onclick="get(this.value);">
<input type="button" class="btn operator" value="+" onclick="get(this.value);">
<br>
<input type="button" class="btn number" value="4" onclick="get(this.value);">
<input type="button" class="btn number" value="5" onclick="get(this.value);">
<input type="button" class="btn number" value="6" onclick="get(this.value);">
<input type="button" class="btn operator" value="*" onclick="get(this.value);">
<br>
<input type="button" class="btn number" value="1" onclick="get(this.value);">
<input type="button" class="btn number" value="2" onclick="get(this.value);">
<input type="button" class="btn number" value="3" onclick="get(this.value);">
<input type="button" class="btn operator" value="-" onclick="get(this.value);">
<br>
<input type="button" class="btn number" value="0" onclick="get(this.value);">
<input type="button" class="btn operator" value="." onclick="get(this.value);">
<input type="button" class="btn operator" value="/" onclick="get(this.value);">
<input type="button" class="btn other" value="=" onclick="calculates();">
</form>
</div>
</body>

...全文

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_MAYAWEN 2018-07-12

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引用 2 楼 foren_whb 的回复:



<!DOCTYPE html />

<html>

<head>

    <title>back space</title>

</head>

<body>

    <input type="number" id="txtTest" value="abc"/>

    <button style="width:90px; height:30px;" onclick="backspace();">backspace</button>

</body>



</html>

<script type="text/javascript">

    function backspace() {

        var o = document.getElementById('txtTest');

        var v = o.value;

        v.length > 0 && (o.value = v.substr(0, v.length - 1));

    }

</script>

我就说原来是我的value已经用过了，声明出了错误。谢谢老哥

丰云 2018-07-12

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<!DOCTYPE html />

<html>

<head>

    <title>back space</title>

</head>

<body>

    <input type="number" id="txtTest" value="abc"/>

    <button style="width:90px; height:30px;" onclick="backspace();">backspace</button>

</body>



</html>

<script type="text/javascript">

    function backspace() {

        var o = document.getElementById('txtTest');

        var v = o.value;

        v.length > 0 && (o.value = v.substr(0, v.length - 1));

    }

</script>