Javascript 图像加载需要一段时间

我有一个打印图像的PHP代码（

echo”“；

），问题是，我第一次运行此代码时，img需要一秒钟的时间才会出现，然后当我刷新浏览器时，图像会立即出现，是否有办法在加载前将img缓存到浏览器？

您无法缓存尚未加载的内容，但是您可以做的是延迟加载映像（例如，使用），或者甚至加载映像的低质量版本，然后使用客户端JS异步加载全质量映像

---

无论哪种方式，图像都必须在缓存之前发送给用户，您只能控制它是否与页面的其余部分同步加载。

您无法缓存尚未加载的内容，但您可以做的是延迟加载图像（例如，使用），或者甚至加载低质量版本的映像，然后使用客户端JS异步加载全质量映像

---

无论哪种方式，图像都必须在缓存之前发送给用户，您只能控制它是否与页面的其余部分同步加载。

有许多技术可以加速图像加载。根据您的场景，它可能是

• 图像精灵
• 图像压缩和正确格式取决于用途
• 图像预加载
• 异步映像加载
• 使用CDN

---

您还可以为图像和其他资源使用单独的子域。

有许多技术可以加速图像加载。根据您的场景，它可能是

• 图像精灵
• 图像压缩和正确格式取决于用途
• 图像预加载
• 异步映像加载
• 使用CDN

---

您还可以为图像和其他资源使用单独的子域。

您可以使用浏览器缓存和Gzip压缩，这将大大提高加载速度

要利用缓存，您可以将以下代码添加到.htaccess

## EXPIRES CACHING ##
<IfModule mod_expires.c>
ExpiresActive On
ExpiresByType image/jpg "access plus 1 year"
ExpiresByType image/jpeg "access plus 1 year"
ExpiresByType image/gif "access plus 1 year"
ExpiresByType image/png "access plus 1 year"
ExpiresByType text/css "access plus 1 month"
ExpiresByType application/pdf "access plus 1 month"
ExpiresByType text/x-javascript "access plus 1 month"
ExpiresByType application/x-shockwave-flash "access plus 1 month"
ExpiresByType image/x-icon "access plus 1 year"
ExpiresDefault "access plus 2 days"
</IfModule>
## EXPIRES CACHING ##

<IfModule mod_deflate.c>
  # Compress HTML, CSS, JavaScript, Text, XML and fonts
  AddOutputFilterByType DEFLATE application/javascript
  AddOutputFilterByType DEFLATE application/rss+xml
  AddOutputFilterByType DEFLATE application/vnd.ms-fontobject
  AddOutputFilterByType DEFLATE application/x-font
  AddOutputFilterByType DEFLATE application/x-font-opentype
  AddOutputFilterByType DEFLATE application/x-font-otf
  AddOutputFilterByType DEFLATE application/x-font-truetype
  AddOutputFilterByType DEFLATE application/x-font-ttf
  AddOutputFilterByType DEFLATE application/x-javascript
  AddOutputFilterByType DEFLATE application/xhtml+xml
  AddOutputFilterByType DEFLATE application/xml
  AddOutputFilterByType DEFLATE font/opentype
  AddOutputFilterByType DEFLATE font/otf
  AddOutputFilterByType DEFLATE font/ttf
  AddOutputFilterByType DEFLATE image/svg+xml
  AddOutputFilterByType DEFLATE image/x-icon
  AddOutputFilterByType DEFLATE text/css
  AddOutputFilterByType DEFLATE text/html
  AddOutputFilterByType DEFLATE text/javascript
  AddOutputFilterByType DEFLATE text/plain
  AddOutputFilterByType DEFLATE text/xml

  # Remove browser bugs (only needed for really old browsers)
  BrowserMatch ^Mozilla/4 gzip-only-text/html
  BrowserMatch ^Mozilla/4\.0[678] no-gzip
  BrowserMatch \bMSIE !no-gzip !gzip-only-text/html
  Header append Vary User-Agent
</IfModule>

##过期缓存##
过期于
过期按类型映像/jpg“访问加1年”
过期按类型图像/jpeg“访问加1年”
ExpiresByType image/gif“访问加1年”
过期按类型图像/png“访问加1年”
ExpiresByType文本/css“访问加1个月”
过期按类型应用程序/pdf“访问加1个月”
ExpiresByType text/x-javascript“访问加1个月”
过期按类型应用程序/x-shockwave-flash“访问加1个月”
过期按类型图像/x图标“访问加1年”
ExpiresDefault“访问加2天”
##过期缓存##

您可以通过向.htaccess添加以下代码来启用Gzip压缩

## EXPIRES CACHING ##
<IfModule mod_expires.c>
ExpiresActive On
ExpiresByType image/jpg "access plus 1 year"
ExpiresByType image/jpeg "access plus 1 year"
ExpiresByType image/gif "access plus 1 year"
ExpiresByType image/png "access plus 1 year"
ExpiresByType text/css "access plus 1 month"
ExpiresByType application/pdf "access plus 1 month"
ExpiresByType text/x-javascript "access plus 1 month"
ExpiresByType application/x-shockwave-flash "access plus 1 month"
ExpiresByType image/x-icon "access plus 1 year"
ExpiresDefault "access plus 2 days"
</IfModule>
## EXPIRES CACHING ##

<IfModule mod_deflate.c>
  # Compress HTML, CSS, JavaScript, Text, XML and fonts
  AddOutputFilterByType DEFLATE application/javascript
  AddOutputFilterByType DEFLATE application/rss+xml
  AddOutputFilterByType DEFLATE application/vnd.ms-fontobject
  AddOutputFilterByType DEFLATE application/x-font
  AddOutputFilterByType DEFLATE application/x-font-opentype
  AddOutputFilterByType DEFLATE application/x-font-otf
  AddOutputFilterByType DEFLATE application/x-font-truetype
  AddOutputFilterByType DEFLATE application/x-font-ttf
  AddOutputFilterByType DEFLATE application/x-javascript
  AddOutputFilterByType DEFLATE application/xhtml+xml
  AddOutputFilterByType DEFLATE application/xml
  AddOutputFilterByType DEFLATE font/opentype
  AddOutputFilterByType DEFLATE font/otf
  AddOutputFilterByType DEFLATE font/ttf
  AddOutputFilterByType DEFLATE image/svg+xml
  AddOutputFilterByType DEFLATE image/x-icon
  AddOutputFilterByType DEFLATE text/css
  AddOutputFilterByType DEFLATE text/html
  AddOutputFilterByType DEFLATE text/javascript
  AddOutputFilterByType DEFLATE text/plain
  AddOutputFilterByType DEFLATE text/xml

  # Remove browser bugs (only needed for really old browsers)
  BrowserMatch ^Mozilla/4 gzip-only-text/html
  BrowserMatch ^Mozilla/4\.0[678] no-gzip
  BrowserMatch \bMSIE !no-gzip !gzip-only-text/html
  Header append Vary User-Agent
</IfModule>

#压缩HTML、CSS、JavaScript、文本、XML和字体
AddOutputFilterByType DEFLATE应用程序/javascript
AddOutputFilterByType DEFLATE应用程序/rss+xml
AddOutputFilterByType DEFLATE应用程序/vnd.ms-fontobject
AddOutputFilterByType放气应用程序/x-font
AddOutputFilterByType放气应用程序/x-font-opentype
AddOutputFilterByType放气应用程序/x-font-otf
AddOutputFilterByType放气应用程序/x-font-truetype
AddOutputFilterByType放气应用程序/x-font-ttf
AddOutputFilterByType DEFLATE应用程序/x-javascript
AddOutputFilterByType DEFLATE应用程序/xhtml+xml
AddOutputFilterByType DEFLATE应用程序/xml
AddOutputFilterByType泄气字体/opentype
AddOutputFilterByType DEFLATE字体/otf
AddOutputFilterByType DEFLATE字体/ttf
AddOutputFilterByType DEFLATE image/svg+xml
AddOutputFilterByType放气图像/x图标
AddOutputFilterByType DEFLATE text/css
AddOutputFilterByType DEFLATE text/html
AddOutputFilterByType DEFLATE text/javascript
AddOutputFilterByType泄气文本/普通
AddOutputFilterByType DEFLATE text/xml
#删除浏览器错误（仅适用于真正旧的浏览器）
浏览器匹配^Mozilla/4 gzip纯文本/html
浏览器匹配^Mozilla/4\.0[678]无gzip
BrowserMatch\bMSIE！没有gzip！仅限gzip文本/html
头附加用户代理

---

您可以同时添加它们，您将看到加载时间的巨大变化。

您可以利用浏览器缓存和Gzip压缩，这将大大提高加载速度

要利用缓存，您可以将以下代码添加到.htaccess

## EXPIRES CACHING ##
<IfModule mod_expires.c>
ExpiresActive On
ExpiresByType image/jpg "access plus 1 year"
ExpiresByType image/jpeg "access plus 1 year"
ExpiresByType image/gif "access plus 1 year"
ExpiresByType image/png "access plus 1 year"
ExpiresByType text/css "access plus 1 month"
ExpiresByType application/pdf "access plus 1 month"
ExpiresByType text/x-javascript "access plus 1 month"
ExpiresByType application/x-shockwave-flash "access plus 1 month"
ExpiresByType image/x-icon "access plus 1 year"
ExpiresDefault "access plus 2 days"
</IfModule>
## EXPIRES CACHING ##

<IfModule mod_deflate.c>
  # Compress HTML, CSS, JavaScript, Text, XML and fonts
  AddOutputFilterByType DEFLATE application/javascript
  AddOutputFilterByType DEFLATE application/rss+xml
  AddOutputFilterByType DEFLATE application/vnd.ms-fontobject
  AddOutputFilterByType DEFLATE application/x-font
  AddOutputFilterByType DEFLATE application/x-font-opentype
  AddOutputFilterByType DEFLATE application/x-font-otf
  AddOutputFilterByType DEFLATE application/x-font-truetype
  AddOutputFilterByType DEFLATE application/x-font-ttf
  AddOutputFilterByType DEFLATE application/x-javascript
  AddOutputFilterByType DEFLATE application/xhtml+xml
  AddOutputFilterByType DEFLATE application/xml
  AddOutputFilterByType DEFLATE font/opentype
  AddOutputFilterByType DEFLATE font/otf
  AddOutputFilterByType DEFLATE font/ttf
  AddOutputFilterByType DEFLATE image/svg+xml
  AddOutputFilterByType DEFLATE image/x-icon
  AddOutputFilterByType DEFLATE text/css
  AddOutputFilterByType DEFLATE text/html
  AddOutputFilterByType DEFLATE text/javascript
  AddOutputFilterByType DEFLATE text/plain
  AddOutputFilterByType DEFLATE text/xml

  # Remove browser bugs (only needed for really old browsers)
  BrowserMatch ^Mozilla/4 gzip-only-text/html
  BrowserMatch ^Mozilla/4\.0[678] no-gzip
  BrowserMatch \bMSIE !no-gzip !gzip-only-text/html
  Header append Vary User-Agent
</IfModule>

##过期缓存##
过期于
过期按类型映像/jpg“访问加1年”
过期按类型图像/jpeg“访问加1年”
ExpiresByType image/gif“访问加1年”
过期按类型图像/png“访问加1年”
ExpiresByType文本/css“访问加1个月”
过期按类型应用程序/pdf“访问加1个月”
ExpiresByType text/x-javascript“访问加1个月”
过期按类型应用程序/x-shockwave-flash“访问加1个月”
过期按类型图像/x图标“访问加1年”
ExpiresDefault“访问加2天”
##过期缓存##

您可以通过向.htaccess添加以下代码来启用Gzip压缩

## EXPIRES CACHING ##
<IfModule mod_expires.c>
ExpiresActive On
ExpiresByType image/jpg "access plus 1 year"
ExpiresByType image/jpeg "access plus 1 year"
ExpiresByType image/gif "access plus 1 year"
ExpiresByType image/png "access plus 1 year"
ExpiresByType text/css "access plus 1 month"
ExpiresByType application/pdf "access plus 1 month"
ExpiresByType text/x-javascript "access plus 1 month"
ExpiresByType application/x-shockwave-flash "access plus 1 month"
ExpiresByType image/x-icon "access plus 1 year"
ExpiresDefault "access plus 2 days"
</IfModule>
## EXPIRES CACHING ##

<IfModule mod_deflate.c>
  # Compress HTML, CSS, JavaScript, Text, XML and fonts
  AddOutputFilterByType DEFLATE application/javascript
  AddOutputFilterByType DEFLATE application/rss+xml
  AddOutputFilterByType DEFLATE application/vnd.ms-fontobject
  AddOutputFilterByType DEFLATE application/x-font
  AddOutputFilterByType DEFLATE application/x-font-opentype
  AddOutputFilterByType DEFLATE application/x-font-otf
  AddOutputFilterByType DEFLATE application/x-font-truetype
  AddOutputFilterByType DEFLATE application/x-font-ttf
  AddOutputFilterByType DEFLATE application/x-javascript
  AddOutputFilterByType DEFLATE application/xhtml+xml
  AddOutputFilterByType DEFLATE application/xml
  AddOutputFilterByType DEFLATE font/opentype
  AddOutputFilterByType DEFLATE font/otf
  AddOutputFilterByType DEFLATE font/ttf
  AddOutputFilterByType DEFLATE image/svg+xml
  AddOutputFilterByType DEFLATE image/x-icon
  AddOutputFilterByType DEFLATE text/css
  AddOutputFilterByType DEFLATE text/html
  AddOutputFilterByType DEFLATE text/javascript
  AddOutputFilterByType DEFLATE text/plain
  AddOutputFilterByType DEFLATE text/xml

  # Remove browser bugs (only needed for really old browsers)
  BrowserMatch ^Mozilla/4 gzip-only-text/html
  BrowserMatch ^Mozilla/4\.0[678] no-gzip
  BrowserMatch \bMSIE !no-gzip !gzip-only-text/html
  Header append Vary User-Agent
</IfModule>

#压缩HTML、CSS、JavaScript、文本、XML和字体
AddOutputFilterByType DEFLATE应用程序/javascript
AddOutputFilterByType DEFLATE应用程序/rss+xml
AddOutputFilterByType DEFLATE应用程序/vnd.ms-fontobject
AddOutputFilterByType放气应用程序/x-font
AddOutputFilterByType放气应用程序/x-font-opentype
AddOutputFilterByType放气应用程序/x-font-otf
AddOutputFilterByType放气应用程序/x-font-truetype
AddOutputFilterByType放气应用程序/x-font-ttf
AddOutputFilterByType DEFLATE应用程序/x-javascript
AddOutputFilterByType DEFLATE应用程序/xhtml+xml
AddOutputFilterByType DEFLATE应用程序/xml
AddOutputFilterByType泄气字体/opentype
AddOutputFilterByType DEFLATE字体/otf
AddOutputFilterByType DEFLATE字体/ttf
AddOutputFilterByType DEFLATE image/svg+xml
AddOutputFilterByType放气图像/x图标
AddOutputFilterByType DEFLATE text/css
AddOutputFilterByType DEFLATE text/html
AddOutputFilterByType DEFLATE text/javascript
AddOutputFilterByType泄气文本/普通
AddOutputFilterByTyp