HTML+CSS3+JS如何实现下拉菜单？本篇文章小编给大家分享一下HTML+CSS3+JS实现下拉菜单代码示例，文章代码介绍的很详细，小编觉得挺不错的，现在分享给大家供大家参考，有需要的小伙伴们可以来看看。

实现效果

html

  
Dropdown Menu
  

    

      First Menu 
      

        
Home
        
About Us
        
Services
        
Contact
      
    
    

      Second Menu 
      

        
Home
        
About Us
        
Services
        
Contact
      
    
    

      Third Menu 
      

        
Home
        
About Us
        
Services
        
Contact
      
    
  
  

    See this same menu only with CSS3: https://codepen.io/pedronauck/pen/jaluz
  

css

@import "compass/css3";

@import url("https://fonts.googleapis.com/css?family=Lato:300,400,700,900");
@import url(https://fonts.googleapis.com/css?family=Pacifico);

body {
	font-family: "Lato", Helvetica, Arial;
	font-size: 16px;
}

.text-center {
  text-align: center;
}

*, *:before, *:after {
	-webkit-border-sizing: border-box;
	-moz-border-sizing: border-box;
	border-sizing: border-box;
}

.container {
	
	margin: 50px auto;
  
  & > ul {
    list-style: none;
    padding: 0;
    margin: 0 0 20px 0;
  }
}

// =============================================================================
//	Mixins and Variables
// =============================================================================

$blue: #2980B9;
$gray: #EEE;

@mixin ul-nostyle {
	list-style: none;
	padding: 0;
	margin: 0;
}

@mixin double-shadow($color) {
	@include box-shadow(0 1px 0 lighten($color, 10%) inset, 0 -1px 0 darken($color, 10%) inset);
}

@mixin hover-style($color) {
	&:hover {
		background: lighten($color, 3%);
	}
}

@mixin animation($content) {
  animation: $content;
  -moz-animation: $content;
  -webkit-animation: $content;
}

@mixin keyframes($name) {
  @keyframes #{$name} { @content; }
  @-moz-keyframes #{$name} { @content; }
  @-webkit-keyframes #{$name} { @content; }
}

// =============================================================================
//	Classes
// =============================================================================

.title {
  font-family: 'Pacifico';
  font-weight: norma;
  font-size: 40px;
  text-align: center;
  line-height: 1.4;
  color: $blue;
}

.dropdown {
	a {
		text-decoration: none;
	}

	[data-toggle="dropdown"] {
		position: relative;
		display: block;
		color: white;
		background: $blue;
		@include double-shadow($blue);
		@include hover-style($blue);
		@include text-shadow(0 -1px 0 rgba(0,0,0,0.3));
		padding: 10px;

	}
	.icon-arrow {
		position: absolute;
		display: block;
		font-size: 0.7em;
		color: #fff;
		top: 14px;
		right: 10px;

		&.open {
			@include transform(rotate(-180deg));
			@include transition(transform .6s);
		}
		&.close {
			@include transform(rotate(0deg));
			@include transition(transform .6s);
		}

		&:before {
			content: '25BC';
		}
	}

	.dropdown-menu {
		max-height: 0;
		overflow: hidden;
		@include ul-nostyle;

		li {
			padding: 0;

			a {
				display: block;
				color: darken($gray, 50%);
				background: $gray;
				@include double-shadow($gray);
				@include hover-style($gray);
				@include text-shadow(0 -1px 0 rgba(255,255,255,0.3));
				padding: 10px 10px;
			}
		}
	}

	.show, .hide {
		@include transform-origin(50%, 0%);
	}

	.show {
		display: block;
		max-
		@include transform(scaleY(1));
		@include animation(showAnimation .5s ease-in-out);
		@include transition(max-height 1s ease-in-out);
	}

	.hide {
		max-height: 0;
		@include transform(scaleY(0));
		@include animation(hideAnimation .4s ease-out);
		@include transition(max-height .6s ease-out);
	}
}

@include keyframes(showAnimation) {
	0% {
		@include transform(scaleY(0.1));
	}
	40% {
		@include transform(scaleY(1.04));
	}
	60% {
		@include transform(scaleY(0.98));
	}
	80% {
		@include transform(scaleY(1.04));
	}
	100% {
		@include transform(scaleY(0.98));
	}				
	80% {
		@include transform(scaleY(1.02));
	}
	100% {
		@include transform(scaleY(1));
	}
}

@include keyframes(hideAnimation) {
  0% {
  	@include transform(scaleY(1));
  }
  60% {
  	@include transform(scaleY(0.98));
  }
  80% {
  	@include transform(scaleY(1.02));
  }
  100% {
  	@include transform(scaleY(0));
  }
}

js

// Dropdown Menu
var dropdown = document.querySelectorAll('.dropdown');
var dropdownArray = Array.prototype.slice.call(dropdown,0);
dropdownArray.forEach(function(el){
	var button = el.querySelector('a[data-toggle="dropdown"]'),
			menu = el.querySelector('.dropdown-menu'),
			arrow = button.querySelector('i.icon-arrow');

	button.onclick = function(event) {
		if(!menu.hasClass('show')) {
			menu.classList.add('show');
			menu.classList.remove('hide');
			arrow.classList.add('open');
			arrow.classList.remove('close');
			event.preventDefault();
		}
		else {
			menu.classList.remove('show');
			menu.classList.add('hide');
			arrow.classList.remove('open');
			arrow.classList.add('close');
			event.preventDefault();
		}
	};
})

Element.prototype.hasClass = function(className) {
    return this.className && new RegExp("(^|s)" + className + "(s|$)").test(this.className);
};