用户输入数字时的Javascript计算器 [英] Javascript calculator as users type numbers

问题描述

我是Java语言的菜鸟，但是我正在尝试在我的网站上实施一些操作，以便用户可以输入数量，并且小计的更新会随着用户的输入而动态更新。
例如：如果每个商品10美元，并且用户在文本字段中键入5，我希望它在文本框旁边显示50美元。非常简单的乘法，但是我不知道如何使用Javascript。我以某种方式认为onKeyPress？谢谢！

I'm a noob at Javascript, but I'm trying to implement something on my website where users can type a quantity, and the subtotal updates dynamically as they type. For example: if items are 10 dollars each, and a user types 5 in the text field I would like it to show $50 next to the text box. Pretty simple multiplication, but I don't know how to do it with Javascript. I think onKeyPress somehow? Thanks!

推荐答案

假定以下HTML：

<input type="text" id="numberField"/>
<span id="result"></span>

JavaScript：

JavaScript:

window.onload = function() {
   var base = 10;
   var numberField = document.getElementById('numberField');
   numberField.onkeyup = numberField.onpaste = function() {
      if(this.value.length == 0) {
         document.getElementById('result').innerHTML = '';
         return;
      }
      var number = parseInt(this.value);
      if(isNaN(number)) return;
      document.getElementById('result').innerHTML = number * base;
   };
   numberField.onkeyup(); //could just as easily have been onpaste();
};

这里是工作示例。

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