表单提交时触发onchange事件

Question

我希望用户能够记录他们执行的操作。我按类别对操作进行了分组，然后使用两个选择菜单和JS，只向用户显示他们选择的类别中的操作。还有一个数量输入，它是根据选择的动作生成的。

我的问题是，当我提交表格时，我会收到错误：

Uncaught TypeError:无法设置null 的属性"onchange">

选择框和JS实现的功能一直工作到表单提交。

index.js

document.addEventListener("DOMContentLoaded", () => {
// First select 
let cat_select = document.getElementById("id_post_cat");
cat_select.onchange = () => handleCatChange(cat_select.value);
// Second select
let desc_select = document.getElementById("id_post_action");
desc_select.onchange = () => handleDescChange(desc_select.value);
});
const handleCatChange = (cat) => {
let quantity_div = document.getElementById("quantity_div");
quantity_div.innerHTML = "";
// Fetching the actions in the category selected and populating second select
fetch(`/action/${cat}`)
.then((response) => response.json())
.then((data) => {
let desc_select = document.getElementById("id_post_action");
let optionHTML = "<option>---------</option>";
data.actions.forEach((action) => {
optionHTML +=
'<option value"' + action.id + '">' + action.desc + "</option>";
});
desc_select.innerHTML = optionHTML;
})
.catch((err) => console.log(err));
};
const handleDescChange = (desc) => {
let quantity_div = document.getElementById("quantity_div");
quantity_div.innerHTML = "";
let time_actions = [
"Public transport instead of driving",
"Walk/cycle instead of drive",
];
let quant_actions = [
"Unplug unused electrical items",
"Repurpose a waste object",
"Use a reusable bag",
"Buy an unpackaged item",
"Buy a locally produced item",
"Buy a second hand item",
"Buy an object in bulk",
"Use a refillable bottle/to-go mug",
"Drink a tap beer instead of bottled beer",
];
if (time_actions.includes(desc)) {
formAdder("Distance* (km)");
} else if (quant_actions.includes(desc)) {
formAdder("Quantity*");
}
};
const formAdder = (label_content) => {
let quantity_div = document.getElementById("quantity_div");
// Label
let label = document.createElement("label");
label.innerHTML = `${label_content}`;
label.setAttribute("for", "id_post_quantity");
label.classList += "requiredField";
// Input
let input = document.createElement("input");
input.setAttribute("id", "id_post_quantity");
input.setAttribute("name", "post_quantity");
input.setAttribute("required", "");
input.classList += "form-control";
quantity_div.append(label, input);
};

views.py

@login_required
def record(request):
if request.method == 'POST':
form = NewPostForm(request.POST)
if form.is_valid():
post = form.save(commit=False)
post.poster = request.user
if request.POST.get('id_post_quantity'):
post.post_quantity = request.POST.get('id_post_quantity')

post.save()
return HttpResponseRedirect(reverse('index'))
return render(request, 'my_app/record.html', {
'form': NewPostForm
})

record.html

<form action="{% url 'record' %}" method="post">
{% csrf_token %}
{{form.post_cat|as_crispy_field}}
{{form.post_action|as_crispy_field}}
<div class="form-group" id="quantity_div">
</div>
<button class="btn btn-success" type="submit">Post</button>
</form>

如果能给我一个正确的指示，我将不胜感激，谢谢。

Answer 1

似乎在加载的每个页面上都调用了onchange。这意味着，当重定向到索引页(其中不存在选择框(时，getElementById返回一个null值等。

我通过添加条件来检查页面上是否存在元素来改变这一点：

document.addEventListener("DOMContentLoaded", () => {
// First select
let cat_select = document.getElementById("id_post_cat");
if (!!cat_select) {
cat_select.onchange = () => handleCatChange(cat_select.value);
}
// Second select
let desc_select = document.getElementById("id_post_action");
if (!!desc_select) {
desc_select.onchange = () => handleDescChange(desc_select.value);
}
});

有没有更优雅/正确的方法来解决同样的问题？

Answer 2

对我来说，当我将提交事件更改为btn-click事件时，它得到了修复。