如果选中复选框，则 JavaScript 添加值

Javascript add value if checkbox is checked

本文关键字：JavaScript 添加 复选框 如果      更新时间：2023-09-26
<p>
    <label for="hours">Learn JavaScript the Hardy Way’ - Complete e-book (Printed)</label>
    <input type="number" min="0" id="chap7" name="hours" value="0">
</p>
<input type="checkbox" id="printed"/>Please tick if you would like a printed version<br />
<p class="post">Postage : <strong>£<output id="post">0</output></strong><p>

我想要一段javascript，以便在选中复选框时，邮费价值为3.50。但是，完整电子书的每本是 3.50。因此，它必须检查数字框的值并将其乘以其中的值。

根据

复选框状态更改的解决方案：

var chap7 = document.getElementById('chap7'),
    post = document.getElementById('post'),
    printed = document.getElementById('printed');
printed.addEventListener('change', function() {
  var quantity = parseInt(chap7.value, 10);
  
  post.value = printed.checked ? quantity * 3.5 : quantity;
}, false);
chap7.addEventListener('change', function() {
  post.value = parseInt(this.value, 10);
});
<p>
    <label for="hours">Learn JavaScript the Hardy Way’ - Complete e-book (Printed)</label>
    <input type="number" min="0" id="chap7" name="hours" value="0">
</p>
<input type="checkbox" id="printed"/>Please tick if you would like a printed version<br />
<p class="post">Postage : <strong>£<output id="post">0</output></strong><p>

根据文本输入状态更改的解决方案：

var chap7 = document.getElementById('chap7'),
    post = document.getElementById('post');
chap7.addEventListener('change', function(e) {
  var quantity = parseInt(chap7.value, 10);
  
  post.value = quantity * 3.5;
}, false);
<p>
    <label for="hours">Learn JavaScript the Hardy Way’ - Complete e-book (Printed)</label>
    <input type="number" min="0" id="chap7" name="hours" value="0">
</p>
<p class="post">Postage : <strong>£<output id="post">0</output></strong><p>

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