![](/img/trans.png)
[英]index.js:8 Uncaught TypeError: Cannot read property 'addEventListener' of undefined at index.js:8,
[英]index.js:28 Uncaught TypeError: Cannot read property 'addEventListener' of null ( at toggleActiveOnClick and at Array.forEach)
對於一個項目,我必須開發一段代碼,但我不能。 這段代碼最初允許我切換某個表單的 4 個可點擊元素,並且效果很好。
const choices = document.querySelectorAll('.clickable');
const toggleActiveClass = (event) => {
event.currentTarget.classList.toggle('active');
};
const toggleActiveOnClick = (choice) => {
choice.addEventListener('click', toggleActiveClass);
};
choices.forEach(toggleActiveOnClick);
但是,現在我必須確保當我 select 前 2 個元素中的一個或另一個時,我不能切換另一個,下一個 2 相同。我嘗試了這段代碼,但是當我在 chrome 工具中打開控制台時我收到這篇文章標題中出現的錯誤消息。 這是有問題的代碼:
const upsell = document.querySelector('.clickable > .fas fa-shopping-cart');
const crossell = document.querySelector('.clickable > .fas fa-cart-plus');
const standard = document.querySelector('.clickable > .fas fa-gift');
const discount = document.querySelector('.clickable > .fas fa-percent');
const choices = [ upsell, crossell, standard, discount ];
const toggleActiveClass = (event) => {
event.currentTarget.classList.toggle('active');
};
const toggleActiveOnClick = (choice) => {
if (choice === upsell.addEventListener('click', toggleActiveClass)) {
crossell.classList.remove('active');
} else if (choice === crossell.addEventListener('click', toggleActiveClass)) {
upsell.classList.remove('active');
} else if (choice === standard.addEventListener('click', toggleActiveClass)) {
discount.classList.remove('active');
} else if (choice === discount.addEventListener('click', toggleActiveClass)) {
standard.classList.remove('active');
}
};
choices.forEach(toggleActiveOnClick);
這里是對應的html
<div class="form-group">
<label for="bundle-type">Bundle Type</label>
<div class="d-flex flex-wrap justify-content-center pt-4">
<div id="test1">
<div class="clickable">
<i class="fas fa-shopping-cart"></i>
<small>Upsell</small>
</div>
</div>
<div id="test2">
<div class="clickable">
<i class="fas fa-cart-plus"></i>
<small>Cros-sell</small>
</div>
</div>
</div>
<label for="bundle-type">Offer Type</label>
<div class="d-flex flex-wrap justify-content-center pt-4">
<div id="test3">
<div class="clickable">
<i class="fas fa-gift"></i>
<small>Standard</small>
</div>
</div>
<div id="test4">
<div class="clickable">
<i class="fas fa-percent"></i>
<small>Discounted</small>
</div>
</div>
</div>
</div>
和 CSS
.clickable i {
font-size: 24px;
margin-bottom: 10px;
}
.clickable:hover i {
color: #167FFB;
}
.clickable.active {
color: inherit;
border-color: inherit;
}
.clickable.active i {
color: #0F60C4;
}
您的選擇器是錯誤的,您可以通過調試/記錄驗證它們( upsell
和其他)。
class="fas fa-shopping-cart"
將兩個類分配給元素fas
和fa-shopping-cart
。 雖然在消化規范后可能有人可以提出多個類的選擇器,但您可以簡單地忽略fas
(對所有類都相同),而 go 則用於特定的類:
console.log("Original attempt:"); const upsell = document.querySelector('.clickable >.fas fa-shopping-cart'); const crossell = document.querySelector('.clickable >.fas fa-cart-plus'); console.log(upsell); console.log(crossell); console.log("Simplified attempt:"); const upsellSimple = document.querySelector('.clickable >.fa-shopping-cart'); const crossellSimple = document.querySelector('.clickable >.fa-cart-plus'); console.log(upsellSimple); console.log(crossellSimple);
<label for="bundle-type">Bundle Type</label> <div class="d-flex flex-wrap justify-content-center pt-4"> <div id="test1"> <div class="clickable"> <i class="fas fa-shopping-cart"></i> <small>Upsell</small> </div> </div> <div id="test2"> <div class="clickable"> <i class="fas fa-cart-plus"></i> <small>Cros-sell</small> </div> </div> </div>
addEventListener()
沒有有意義的返回值:
返回值:
undefined
比較( if (choice === xy.addEventListener(...)){...}
)並不能真正做任何有用的事情。
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