遊戲陪玩系統原始碼中懶載入的實現方式有哪幾種？

雲豹科技程式設計師發表於2021-10-18
遊戲原始碼

遊戲陪玩系統原始碼的載入速度對使用者的使用體驗影響還是比較大的，畢竟頁面內容載入過慢的話，會讓使用者喪失耐心，導致使用者流量的流失，所以為了優化載入速度，在遊戲陪玩系統原始碼開發時，可以選擇懶載入的方式。

遊戲陪玩系統原始碼採用懶載入方式的優勢

1、效能收益：移動裝置端載入圖片、decode、渲染都需要耗費資源，懶載入能節約效能消耗，縮短onload事件時間。
2、節約頻寬：這個不需要解釋。

通常，我們在html中展示圖片，會有兩種方式：

1、img 標籤
2、css background-image

img的懶載入實現

img有兩種方式實現懶載入：

1、事件監聽(scroll、resize、orientationChange)

<!DOCTYPE html><html lang="en"><head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>event</title>
    <style>
        img {
            background: #F1F1FA;
            width: 400px;
            height: 300px;
            display: block;
            margin: 10px auto;
            border: 0;
        }
    </style></head><body>
    <img src="https://ik.imagekit.io/demo/img/image1.jpeg?tr=w-400,h-300" />
    <img src="https://ik.imagekit.io/demo/img/image2.jpeg?tr=w-400,h-300" />
    <img src="https://ik.imagekit.io/demo/img/image3.jpg?tr=w-400,h-300" />
    <img class="lazy" data-src="https://ik.imagekit.io/demo/img/image2.jpeg?tr=w-400,h-300" />
    <img class="lazy" data-src="https://ik.imagekit.io/demo/img/image3.jpg?tr=w-400,h-300" /> -->
    <img class="lazy" data-src="https://ik.imagekit.io/demo/img/image4.jpeg?tr=w-400,h-300" />
    <img class="lazy" data-src="https://ik.imagekit.io/demo/img/image5.jpeg?tr=w-400,h-300" />
    <img class="lazy" data-src="https://ik.imagekit.io/demo/img/image6.jpeg?tr=w-400,h-300" />
    <img class="lazy" data-src="https://ik.imagekit.io/demo/img/image7.jpeg?tr=w-400,h-300" />
    <img class="lazy" data-src="https://ik.imagekit.io/demo/img/image8.jpeg?tr=w-400,h-300" />
    <img class="lazy" data-src="https://ik.imagekit.io/demo/img/image9.jpeg?tr=w-400,h-300" />
    <img class="lazy" data-src="https://ik.imagekit.io/demo/img/image10.jpeg?tr=w-400,h-300" />
    <script>
        document.addEventListener("DOMContentLoaded", function() {
            var lazyloadImages = document.querySelectorAll("img.lazy");    
            var lazyloadThrottleTimeout;
            
            function lazyload () {
                if(lazyloadThrottleTimeout) {
                    clearTimeout(lazyloadThrottleTimeout);
                }    
                
                lazyloadThrottleTimeout = setTimeout(function() {
                    var scrollTop = window.pageYOffset;
                    lazyloadImages.forEach(function(img) {
                        if(img.offsetTop < (window.innerHeight + scrollTop)) {
                            img.src = img.dataset.src;
                            img.classList.remove('lazy');
                        }
                    });
                    if(lazyloadImages.length == 0) {
                        document.removeEventListener("scroll", lazyload);
                        window.removeEventListener("resize", lazyload);
                        window.removeEventListener("orientationChange", lazyload);
                    }
                }, 20);
            }
            
            document.addEventListener("scroll", lazyload);
            window.addEventListener("resize", lazyload);
            window.addEventListener("orientationChange", lazyload);
        });
    </script></body></html>

2、Intersection Observer（相容性問題）

<!DOCTYPE html><html lang="en"><head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>observer</title>
    <style>
        img {
            background: #F1F1FA;
            width: 400px;
            height: 300px;
            display: block;
            margin: 10px auto;
            border: 0;
        }
    </style></head><body>
    <img src="https://ik.imagekit.io/demo/img/image2.jpeg?tr=w-400,h-300" />
    <img src="https://ik.imagekit.io/demo/img/image3.jpg?tr=w-400,h-300" /> -->
    <img class="lazy" data-src="https://ik.imagekit.io/demo/img/image1.jpeg?tr=w-400,h-300" />
    <img class="lazy" data-src="https://ik.imagekit.io/demo/img/image2.jpeg?tr=w-400,h-300" />
    <img class="lazy" data-src="https://ik.imagekit.io/demo/img/image3.jpg?tr=w-400,h-300" />
    <img class="lazy" data-src="https://ik.imagekit.io/demo/img/image4.jpeg?tr=w-400,h-300" />
    <img class="lazy" data-src="https://ik.imagekit.io/demo/img/image5.jpeg?tr=w-400,h-300" />
    <img class="lazy" data-src="https://ik.imagekit.io/demo/img/image6.jpeg?tr=w-400,h-300" />
    <img class="lazy" data-src="https://ik.imagekit.io/demo/img/image7.jpeg?tr=w-400,h-300" />
    <img class="lazy" data-src="https://ik.imagekit.io/demo/img/image8.jpeg?tr=w-400,h-300" />
    <img class="lazy" data-src="https://ik.imagekit.io/demo/img/image9.jpeg?tr=w-400,h-300" />
    <img class="lazy" data-src="https://ik.imagekit.io/demo/img/image10.jpeg?tr=w-400,h-300" />
    <script>
        document.addEventListener("DOMContentLoaded", function() {
            var lazyloadImages = document.querySelectorAll(".lazy");
            var imageObserver = new IntersectionObserver(function(entries, observer) {
                entries.forEach(function(entry) {
                    if (entry.isIntersecting) {
                        var image = entry.target;
                        image.src = image.dataset.src;
                        image.classList.remove("lazy");
                        imageObserver.unobserve(image);
                    }
                });
            });
            lazyloadImages.forEach(function(image) {
                imageObserver.observe(image);
            });
        });
    </script></body></html>

background-image的實現

background-image的實現跟img的原理基本是一樣的，區別是在對class的處理上：

<!DOCTYPE html><html lang="en"><head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>background</title>
    <style>
        body {
            margin: 0;
        }
        .bg {
            height: 200px;
        }
        #bg-image.lazy {
            background-image: none;
            background-color: #F1F1FA;
        }
        #bg-image {
            background-image: url("https://ik.imagekit.io/demo/img/image1.jpeg?tr=w-400,h-300");
            background-size: 100%;
        }
    </style></head><body>
    <div id="bg-image" class="bg lazy"></div>
    <div id="bg-image" class="bg lazy"></div>
    <div id="bg-image" class="bg lazy"></div>
    <div id="bg-image" class="bg lazy"></div>
    <div id="bg-image" class="bg lazy"></div>
    <div id="bg-image" class="bg lazy"></div>
    <div id="bg-image" class="bg lazy"></div>
    <div id="bg-image" class="bg lazy"></div>
    <script>
        document.addEventListener("DOMContentLoaded", function() {
            var lazyloadImages = document.querySelectorAll(".lazy");
            var imageObserver = new IntersectionObserver(function(entries, observer) {
                entries.forEach(function(entry) {
                    if (entry.isIntersecting) {
                        var image = entry.target;
                        image.classList.remove("lazy");
                        imageObserver.unobserve(image);
                    }
                });
            });
            lazyloadImages.forEach(function(image) {
                imageObserver.observe(image);
            });
        });
    </script></body></html>

漸進式懶載入

遊戲陪玩系統原始碼的漸進式懶載入，指的是存在降級處理，通常html形式如下：

<a href="full.jpg" class="progressive replace">
  <img src="tiny.jpg" class="preview" alt="image" /></a>

這樣的程式碼會有2個好處：

1、如果js執行失敗，可以點選預覽
2、大小與遊戲陪玩系統原始碼實際圖一致的佔位data URI，避免reflow
最終的程式碼如下：

<!DOCTYPE html><html lang="en"><head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>progressive</title>
    <style>
        a.progressive {
            position: relative;
            display: block;
            overflow: hidden;
            outline: none;
        }
        a.progressive:not(.replace) {
            cursor: default;
        }
        a.progressive img {
            display: block;
            width: 100%;
            max-width: none;
            height: auto;
            border: 0 none;
        }
        a.progressive img.preview {
            filter: blur(2vw);
            transform: scale(1.05);
        }
        a.progressive img.reveal {
            position: absolute;
            left: 0;
            top: 0;
            will-change: transform, opacity;
            animation: reveal 1s ease-out;
        }
        @keyframes reveal {
            0% {transform: scale(1.05); opacity: 0;}
            100% {transform: scale(1); opacity: 1;}
        }
    </style></head><body>
    <a href="
        <img src="data:image/jpeg;base64,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" class="preview" alt="palm trees" />
    </a>
    <a href="
        <img src="
    </a>
    <a href="
        <img src="
    </a>
    <a href="
        <img src="data:image/jpeg;base64,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" class="preview" alt="palm trees" />
    </a>
    <a href="
        <img src="
    </a>
    <a href="
        <img src="
    </a>
    <script>
        window.addEventListener('load', function() {
            var pItem = document.getElementsByClassName('progressive replace'), timer;
            window.addEventListener('scroll', scroller, false);
            window.addEventListener('resize', scroller, false);
            inView();
            function scroller(e) {
                timer = timer || setTimeout(function() {
                    timer = null;
                    requestAnimationFrame(inView);
                }, 300);
            }
            function inView() {
                var scrollTop = window.pageYOffset;
                var innerHeight = window.innerHeight;
                var p = 0;
                while (p < pItem.length) {
                    var offsetTop = pItem[p].offsetTop;
                    if (offsetTop < (scrollTop + innerHeight)) {
                        loadFullImage(pItem[p]);
                        pItem[p].classList.remove('replace');
                    }
                    else p++;
                }
            }
            function loadFullImage(item) {
                var img = new Image();
                if (item.dataset) {
                    img.srcset = item.dataset.srcset || '';
                    img.sizes = item.dataset.sizes || '';
                }
                img.src = item.href;
                img.className = 'reveal';
                if (img.complete) addImg();
                else img.onload = addImg;
                function addImg() {
                    item.addEventListener('click', function(e) { e.preventDefault(); }, false);
                    item.appendChild(img).addEventListener('animationend', function(e) {
                        var pImg = item.querySelector('img.preview');
                        if (pImg) {
                            e.target.alt = pImg.alt || '';
                            item.removeChild(pImg);
                            e.target.classList.remove('reveal');
                        }
                    });
                }
            }
        }, false);
    </script></body></html>

以上便是“遊戲陪玩系統原始碼中懶載入的3種實現方式”的全部內容，希望對大家有幫助。

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原文連結：


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