如果復選框被選中，Javascript 添加值

Question

<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，以便在選中復選框時，郵資值為3.50。 但是，完整電子書的每份 3.50 美元。 所以它必須檢查數字框的值並按里面的值對其進行計時。

Answer 1

根據復選框狀態更改的解決方案：

 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>

---

根據文本輸入狀態變化的解決方案：

 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>