HTMLImageElement.sizes

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句法
范例
规范
浏览器兼容性
另请参阅
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HTMLImageElement property sizes allows you to specify the layout width of the image for each of a list of media conditions. This provides the ability to automatically select among different images—even images of different orientations or aspect ratios—as the document state changes to match different media conditions. Each condition is specified using the same conditional format used by media queries .

句法

let sizes = htmlImageElement.sizes;
htmlImageElement.sizes = sizes;

值

A USVString containing a comma-separated list of source size descriptors followed by an optional fallback size. Each source size descriptor is comprised of a media condition, then at least one whitespace character, then the source size value to use for the image when the media condition evaluates to true .

Media conditions

Each source size descriptor consists of a media condition as defined by the media queries standard. Because a source size descriptor is used to specify the width to use for the image during layout of the page, the media condition is typically (but not necessarily) based entirely on width information. See 句法 in Using media queries for details on how to construct a media condition.

Source size values

The source size value is a CSS length . It may be specified using font-relative units (such as em or ex ), absolute units (such as px or cm ), or the vw unit, which lets you specify the width as a percentage of the viewport width ( 1vw being 1% of the viewport width).

注意： The source size value must not be specified as a percentage of the container size; that is, lengths such as 50% or 100% are not allowed, as there would be uncertainty as to what the specified value is a percentage of.

范例

In this example, a blog-like layout is created, displaying some text and an image which for which three size points are specified, depending on the width of the window. Three versions of the image are also available, with their widths specified. The browser takes all of this information and selects an image and width that best meets the specified values.

How exactly the images are used may depend upon the browser and what the pixel density of the user's display is.

Buttons at the bottom of the example let you actually modify the sizes property slightly, switching the largest of the three widths for the image between 40em and 50em.

HTML

<article>
  <h1>An amazing headline</h1>
  <div class="test"></div>
  <p>This is even more amazing content text. It's really spectacular.
     And fascinating. Oh, it's also clever and witty. Award-winning
     stuff, I'm sure.</p>
  <img src="/files/16870/new-york-skyline-wide.jpg"
       srcset="/files/16870/new-york-skyline-wide.jpg 3724w,
               /files/16869/new-york-skyline-4by3.jpg 1961w,
               /files/16871/new-york-skyline-tall.jpg 1060w"
       sizes="((min-width: 50em) and (max-width: 60em)) 50em,
              ((min-width: 30em) and (max-width: 50em)) 30em,
              (max-width: 30em) 20em">
  <p>Then there's even more amazing stuff to say down here. Can you
     believe it? I sure can't.</p>
  <button id="break40">Last Width: 40em</button>
  <button id="break50">Last Width: 50em</button>
</article>

CSS

article {
  margin: 1em;
  max-width: 60em;
  min-width: 20em;
  height: 100vh;
  border: 4em solid #880E4F;
  border-radius: 7em;
  padding: 1.5em;
  font: 16px "Open Sans", Verdana, Arial, Helvetica, sans-serif;
}
article img {
  display: block;
  max-width: 100%;
  border: 1px solid #888;
  box-shadow: 0 0.5em 0.3em #888;
  margin-bottom: 1.25em;
}

JavaScript

The JavaScript code handles the two buttons that let you toggle the third width option between 40em and 50em; this is done by handling the click event, using the JavaScript string object method replace() to replace the relevant portion of the sizes 字符串。

let image = document.querySelector("article img");
let break40 = document.getElementById("break40");
let break50 = document.getElementById("break50");
break40.addEventListener("click",
    event => image.sizes = image.sizes.replace(/50em,/, "40em,"));
break50.addEventListener("click",
    event => image.sizes = image.sizes.replace(/40em,/, "50em,"));

结果

This result may be viewed in its own window here .

规范

规范	状态	注释
HTML 实时标准 The definition of 'HTMLImageElement.sizes' in that specification.	实时标准

浏览器兼容性

The compatibility table on this page is generated from structured data. If you'd like to contribute to the data, please check out https://github.com/mdn/browser-compat-data and send us a pull request. 更新 GitHub 上的兼容性数据

	桌面						移动
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	Android webview	Chrome for Android	Firefox for Android	Opera for Android	Safari on iOS	Samsung Internet
`sizes`	Chrome 45	Edge 13	Firefox 38 38 不支持 33 — 52 Disabled Disabled ). To change preferences in Firefox, visit	IE No	Opera Yes	Safari No	WebView Android 45	Chrome Android 45	Firefox Android 38 38 不支持 33 — 52 Disabled Disabled ). To change preferences in Firefox, visit	Opera Android No	Safari iOS No	Samsung Internet Android 5.0

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句法

值

Media conditions

Source size values

范例

HTML

CSS

JavaScript

结果

规范

浏览器兼容性

图例

另请参阅

元数据

相关话题