【lazyload】たったひとつのタグで画像・iframeを遅延読み込みできる方法を教えるよ
Tags: wordpress, javascript, lazyload
Published: 2020-02-13 08:09:36

## はじめに
この方法はWordPressなどで使うと効果的です。

まずはじめに、`</body>` 直前に下記のScriptを挿入してください。場合によっては`<head> ~ </head>`内に挿入。

`</body>`の直前の理由は、少しでも読み込みスピードの足を引っ張らないようにするためです。

ここに関してはあなたのやり方に任せます。

```

<script>
!function(a,b){var c=b(a,a.document,Date);a.lazySizes=c,"object"==typeof module&&module.exports&&(module.exports=c)}("undefined"!=typeof window?window:{},function(a,b,c){"use strict";var d,e;if(function(){var b,c={lazyClass:"lazyload",loadedClass:"lazyloaded",loadingClass:"lazyloading",preloadClass:"lazypreload",errorClass:"lazyerror",autosizesClass:"lazyautosizes",srcAttr:"data-src",srcsetAttr:"data-srcset",sizesAttr:"data-sizes",minSize:40,customMedia:{},init:!0,expFactor:1.5,hFac:.8,loadMode:2,loadHidden:!0,ricTimeout:0,throttleDelay:125};e=a.lazySizesConfig||a.lazysizesConfig||{};for(b in c)b in e||(e[b]=c[b])}(),!b||!b.getElementsByClassName)return{init:function(){},cfg:e,noSupport:!0};var f=b.documentElement,g=a.HTMLPictureElement,h="addEventListener",i="getAttribute",j=a[h].bind(a),k=a.setTimeout,l=a.requestAnimationFrame||k,m=a.requestIdleCallback,n=/^picture$/i,o=["load","error","lazyincluded","_lazyloaded"],p={},q=Array.prototype.forEach,r=function(a,b){return p[b]||(p[b]=new 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</script>

```

## classの挿入、srcの書き換え
次に、遅延読み込みをさせたい対象に次のclassを入れてください

```

class="lazyload"

```

最後に src　を次のように書き換えてください。
```

data-src

```

### imgの例
```

<img data-src="xxx.png" class="lazyload" alt="xxx">

```

iframe（google map , youtube etc...）の場合も同様の形で書き換え、classの追記をしてください。


おめでとう。これで遅延読み込みの実装は完了だ。