CSS之hover的使用和鼠标移入移出事件的区别、addEventListener、mouseenter、mouseleave、querySelector、split、+、~

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1、作用于自身

.oneself:hover {
	color: #0000ff;
}

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<div class='oneself'>作用于自身</div>

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2、作用于子元素

.child_element_box:hover>.child_element {
	color: #0000ff;
}

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<div class="child_element_box">
	<div class="child_element">作用于子元素</div>
</div>

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3、作用于兄弟元素

选择下一个紧挨的兄弟元素

.be_next_to_closely:hover+div {
	color: #0000ff;
}

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<div>
	<div class="be_next_to_closely">选择紧挨的兄弟元素</div>
	<div>紧挨着的元素</div>
	<div>不是紧挨着的元素</div>
</div>

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选择后边所有符合条件的兄弟元素

.all_element:hover~.elements {
	color: #0000ff;
}

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<div>
	<div class="all_element">选择后边所有符合条件的兄弟元素</div>
	<div class="elements">符合的元素1</div>
	<div>不符合的元素1</div>
	<div class="elements">符合的元素2</div>
</div>

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4、使用JavaScript配合CSS实现样式修改

.box {
	width: 100%;
	height: calc(100vh - 17px);
	background-image: url('./img/by01.jpg');
}

.tab_bar_box {
	position: fixed;
	left: 50%;
	top: 50%;
	transform: translate(-50%, -50%);
}

.tab_bar_box>span {
	display: inline-block;
	width: 130px;
	border: 1px solid #777777;
	border-radius: 7px;
	padding: 7px;
	margin: 0;
	text-align: center;
	cursor: pointer;
	background-color: #eeeeee;
	opacity: .3;
}

.tab_bar_box>span:nth-child(2) {
	margin: 0 68px;
}

.tab_bar_1:hover,
.tab_bar_2:hover,
.tab_bar_3:hover {
	color: #0000ff;
	font-weight: 700;
	border: 1px solid #0000ff;
	opacity: .7;
}

---

<div class="box">
	<div class="tab_bar_box">
		<span class="tab_bar_1">标签1</span>
		<span class="tab_bar_2">标签2</span>
		<span class="tab_bar_3">标签3</span>
	</div>
</div>

---

(function () {
	let tabBar1 = document.querySelector('.tab_bar_1'),
		tabBar2 = document.querySelector('.tab_bar_2'),
		tabBar3 = document.querySelector('.tab_bar_3'),
		box = document.querySelector('.box');
	
	tabBar1.addEventListener("mouseenter", mouseenter, false);
	tabBar1.addEventListener("mouseleave", mouseleave, false);
	
	tabBar2.addEventListener("mouseenter", mouseenter, false);
	tabBar2.addEventListener("mouseleave", mouseleave, false);
	
	tabBar3.addEventListener("mouseenter", mouseenter, false);
	tabBar3.addEventListener("mouseleave", mouseleave, false);
	
	function mouseenter(e) {
		let indexArr = e.target.className.split('_'),
			i = indexArr[indexArr.length - 1],
			arr = ["url('./img/by07.jpg')", "url('./img/by09.jpg')", "url('./img/by12.jpg')"];
		
		box.style.backgroundImage = arr[i - 1];
		box.style.transitionDuration = '.7s';
	}
	
	function mouseleave() {
		box.style.backgroundImage = `url('./img/by01.jpg')`;
		box.style.transitionDuration = '.7s';
	}
})();

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5、鼠标移入移出事件的区别

移入事件

mouseover：不论鼠标指针穿过被选元素或其子元素，都会触发mouseover事件。对应mouseout
mouseenter：只有在鼠标指针穿过被选元素时，才会触发mouseenter事件。对应mouseleave

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鼠标移出事件

mouseout：不论鼠标指针离开被选元素还是任何子元素，都会触发mouseout事件
mouseleave：只有在鼠标指针离开被选元素时，才会触发mouseleave事件