如何使用循环压缩JavaScript

Question

我有以下代码可以正常工作，以响应页面上多个div的延迟加载背景图像：

// get frames
// REFACTOR LIST:
var frame1 = document.getElementById('frame1');
var frame2 = document.getElementById('frame2');
var frame3 = document.getElementById('frame3');
var frame4 = document.getElementById('frame4');
var frame5 = document.getElementById('frame5');
// create Lazy loader
var myLazyLoad = new LazyLoad({
elements_selector: ".lazy"
});
// load images responsively
function loadImgs() {

console.log('Loading images...');

if(window.matchMedia("only screen and (max-width:700px)").matches) {
// viewport is less than or equal to 700 pixels wide
// REFACTOR LIST:
var src1 = frame1.getAttribute('data-src-small');
var src2 = frame2.getAttribute('data-src-small');
var src3 = frame3.getAttribute('data-src-small');
var src4 = frame4.getAttribute('data-src-small');
var src5 = frame5.getAttribute('data-src-small');
} else {
// viewport is greater than 700 pixels wide
// REFACTOR LIST:
var src1 = frame1.getAttribute('data-src-large');
var src2 = frame2.getAttribute('data-src-large');
var src3 = frame3.getAttribute('data-src-large');
var src4 = frame4.getAttribute('data-src-large');
var src5 = frame5.getAttribute('data-src-large');
} 
// set data-src for lazy loader
// REFACTOR LIST:
frame1.setAttribute('data-src', src1);
frame2.setAttribute('data-src', src2);
frame3.setAttribute('data-src', src3);
frame4.setAttribute('data-src', src4);
frame5.setAttribute('data-src', src5);

// tell lazy loader that the data should be re-processed
// REFACTOR LIST:
frame1.removeAttribute('data-was-processed');
frame2.removeAttribute('data-was-processed');
frame3.removeAttribute('data-was-processed');
frame4.removeAttribute('data-was-processed');
frame5.removeAttribute('data-was-processed'); 
// tell lazy loader to update
myLazyLoad.update();
}
// load images initially
loadImgs();
// reload images when window is resized across the 700px breakpoint
var lastWindowSize = window.innerWidth;
window.onresize = function(event) {
var currentWindowSize = window.innerWidth; 
if((lastWindowSize <= 700 && currentWindowSize > 700) || (lastWindowSize > 700 && currentWindowSize <= 700)) {
loadImgs();
}
lastWindowSize = currentWindowSize;
};

html {
box-sizing: border-box;
}
*, *::before, *::after {
box-sizing: inherit;
&:focus {
outline: none;
}
}
* {
font-family: monaco, courier;
}
body {
margin: 0;
padding: 0;
}
.wrapper {
width: 100%;
min-height: 100vh;
display: flex;
flex-direction: column;
align-items: center;
justify-content: center ;
background: #ddd;
}
p {
position: absolute;
top: 0;
left: 0;
margin: 0;
padding: 8px;
color: darkslategray;
background: gold;
}
.frame {
width: 80vw;
height: 200px;
margin: 0 0 1rem 0;
padding: 0;
position: relative;
background-size: cover;
background-position: center;
background-repeat: no-repeat;
border: 2px solid gold;
}

<script src="https://cdnjs.cloudflare.com/ajax/libs/vanilla-lazyload/8.7.1/lazyload.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.5.1/jquery.min.js"></script>
<!-- https://stackoverflow.com/questions/50431531/lazylaoding-css-background-not-html-img-tags -->
<main class="wrapper">
<a href="#">
<div id="frame1" class="frame lazy" 
data-src-small="https://source.unsplash.com/random/400x200?sig=1"
data-src-large="https://source.unsplash.com/random/1200x600?sig=1">
<p>1</p>
</div>
</a>
<a href="#">
<div id="frame2" class="frame lazy" 
data-src-small="https://source.unsplash.com/random/400x200?sig=2"
data-src-large="https://source.unsplash.com/random/1200x600?sig=2">
<p>2</p>
</div>
</a>
<a href="#">
<div id="frame3" class="frame lazy" 
data-src-small="https://source.unsplash.com/random/400x200?sig=3"
data-src-large="https://source.unsplash.com/random/1200x600?sig=3">
<p>3</p>
</div>
</a>
<a href="#">
<div id="frame4" class="frame lazy" 
data-src-small="https://source.unsplash.com/random/400x200?sig=4"
data-src-large="https://source.unsplash.com/random/1200x600?sig=4">
<p>4</p>
</div>
</a>
<a href="#">
<div id="frame5" class="frame lazy" 
data-src-small="https://source.unsplash.com/random/400x200?sig=5"
data-src-large="https://source.unsplash.com/random/1200x600?sig=5">
<p>5</p>
</div>
</a>
</main>

CodePen此处

但我想重构代码以使其变干。我认为for循环可以用来替换REFACTOR LIST:注释下的5个列表中的每一个。我的目标是为frame类的任何未知数量的div启用代码。

首先，作为一个例子，我尝试在开始时用以下循环重构变量声明：

var FramesQuantity = document.getElementsByClassName("frame").length
var frameVariables = [];
function createframeVariables() {
for (var i = 0; i <= FramesQuantity; ++i) {
var frameIndex = 'frame' + i;
console.log("frameIndex: " + frameIndex);
frameVariables[i] = document.getElementById(frameIndex);
}
return frameVariables;
}
createframeVariables();
console.log("frameVariables[0]: " + frameVariables[0]);

但第二个控制台日志返回CCD_ 3，我不确定这是否是正确的方向。

有什么想法吗？

Answer 1

正如建议的那样，我可以通过使用.forEach和.querySelectorAll来重构代码，从而避免设置变量：

// for loop demo
document.querySelectorAll('.frame[data-src-small]').forEach( (frame, index) => {
console.log( "index: " + index);
console.log( "frame.dataset.srcSmall: " + frame.dataset.srcSmall);
console.log( "frame.dataset.srcLarge: " + frame.dataset.srcLarge);
})
// create Lazy loader
var myLazyLoad = new LazyLoad({
elements_selector: ".lazy"
});
// load images responsively
function loadImgs(context) {
console.log('Loading images ' + context);

if(window.matchMedia("only screen and (max-width:700px)").matches) {
// viewport is less than or equal to 700 pixels wide
document.querySelectorAll('.frame[data-src-small]').forEach( (frame, index) => {
var srcSmall = frame.dataset.srcSmall;
// set data-src for lazy loader
frame.setAttribute('data-src', srcSmall);
// tell lazy loader that the data should be re-processed
frame.removeAttribute('data-was-processed');
})
} else {
document.querySelectorAll('.frame[data-src-small]').forEach( (frame, index) => {
// viewport is greater than 700 pixels wide
var srcLarge = frame.dataset.srcLarge;
// set data-src for lazy loader
frame.setAttribute('data-src', srcLarge);
// tell lazy loader that the data should be re-processed
frame.removeAttribute('data-was-processed');
})
} 

// tell lazy loader to update
myLazyLoad.update();
}
// load images initially
loadImgs("initially");
// reload images when window is resized across the 700px breakpoint
var lastWindowSize = window.innerWidth;
window.onresize = function(event) {
var currentWindowSize = window.innerWidth; 
if((lastWindowSize <= 700 && currentWindowSize > 700) || (lastWindowSize > 700 && currentWindowSize <= 700)) {
loadImgs("on resize across breakpoint");
}
lastWindowSize = currentWindowSize;
};

在此处分叉原始CodePen的更新版本。