HTMLImageElement - Web APIs 编辑

The HTMLImageElement interface represents an HTML <img> element, providing the properties and methods used to manipulate image elements.

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Constructor

Image()

The Image() constructor creates and returns a new HTMLImageElement object representing an HTML <img> element which is not attached to any DOM tree. It accepts optional width and height parameters. When called without parameters, new Image() is equivalent to calling document.createElement("img").

Properties

Inherits properties from its parent, HTMLElement.

HTMLImageElement.alt

A DOMString that reflects the alt HTML attribute, thus indicating the alternate fallback content to be displayed if the image has not been loaded.

HTMLImageElement.complete Read only

Returns a Boolean that is true if the browser has finished fetching the image, whether successful or not. That means this value is also true if the image has no src value indicating an image to load.

HTMLImageElement.crossOrigin

A DOMString specifying the CORS setting for this image element. See CORS settings attributes for further details. This may be null if CORS is not used.

HTMLImageElement.currentSrc Read only

Returns a USVString representing the URL from which the currently displayed image was loaded. This may change as the image is adjusted due to changing conditions, as directed by any media queries which are in place.

HTMLImageElement.decoding

An optional DOMString representing a hint given to the browser on how it should decode the image. If this value is provided, it must be one of the possible permitted values: sync to decode the image synchronously, async to decode it asynchronously, or auto to indicate no preference (which is the default). Read the decoding page for details on the implications of this property's values.

HTMLImageElement.height

An integer value that reflects the height HTML attribute, indicating the rendered height of the image in CSS pixels.

HTMLImageElement.isMap

A Boolean that reflects the ismap HTML attribute, indicating that the image is part of a server-side image map. This is different from a client-side image map, specified using an <img> element and a corresponding <map> which contains <area> elements indicating the clickable areas in the image. The image must be contained within an <a> element; see the ismap page for details.

HTMLImageElement.loading

A DOMString providing a hint to the browser used to optimize loading the document by determining whether to load the image immediately (eager) or on an as-needed basis (lazy).

HTMLImageElement.naturalHeight Read only

Returns an integer value representing the intrinsic height of the image in CSS pixels, if it is available; else, it shows 0. This is the height the image would be if it were rendered at its natural full size.

HTMLImageElement.naturalWidth Read only

An integer value representing the intrinsic width of the image in CSS pixels, if it is available; otherwise, it will show 0. This is the width the image would be if it were rendered at its natural full size.

HTMLImageElement.referrerPolicy

A DOMString that reflects the referrerpolicy HTML attribute, which tells the user agent how to decide which referrer to use in order to fetch the image. Read this article for details on the possible values of this string.

HTMLImageElement.sizes

A DOMString reflecting the sizes HTML attribute. This string specifies a list of comma-separated conditional sizes for the image; that is, for a given viewport size, a particular image size is to be used. Read the documentation on the sizes page for details on the format of this string.

HTMLImageElement.src

A USVString that reflects the src HTML attribute, which contains the full URL of the image including base URI. You can load a different image into the element by changing the URL in the src attribute.

HTMLImageElement.srcset

A USVString reflecting the srcset HTML attribute. This specifies a list of candidate images, separated by commas (',', U+002C COMMA). Each candidate image is a URL followed by a space, followed by a specially-formatted string indicating the size of the image. The size may be specified either the width or a size multiple. Read the srcset page for specifics on the format of the size substring.

HTMLImageElement.useMap

A DOMString reflecting the usemap HTML attribute, containing the page-local URL of the <map> element describing the image map to use. The page-local URL is a pound (hash) symbol (#) followed by the ID of the <map> element, such as #my-map-element. The <map> in turn contains <area> elements indicating the clickable areas in the image.

HTMLImageElement.width

An integer value that reflects the width HTML attribute, indicating the rendered width of the image in CSS pixels.

HTMLImageElement.x Read only

An integer indicating the horizontal offset of the left border edge of the image's CSS layout box relative to the origin of the <html> element's containing block.

HTMLImageElement.y Read only

The integer vertical offset of the top border edge of the image's CSS layout box relative to the origin of the <html> element's containing block.

Obsolete properties

HTMLImageElement.align

A DOMString indicating the alignment of the image with respect to the surrounding context. The possible values are "left", "right", "justify", and "center". This is obsolete; you should instead use CSS (such as text-align, which works with images despite its name) to specify the alignment.

HTMLImageElement.border

A DOMString which defines the width of the border surrounding the image. This is deprecated; use the CSS border property instead.

HTMLImageElement.hspace

An integer value which specifies the amount of space (in pixels) to leave empty on the left and right sides of the image.

HTMLImageElement.longDesc

A USVString specifying the URL at which a long description of the image's contents may be found. This is used to turn the image into a hyperlink automatically. Modern HTML should instead place an <img> inside an <a> element defining the hyperlink.

HTMLImageElement.lowsrc

A USVString specifying the URL of a low-quality (but faster to load) version of the same image. This was once used by browsers under constrained network conditions or on slow devices.

HTMLImageElement.name

A DOMString representing the name of the element.

HTMLImageElement.vspace

An integer value specifying the amount of empty space, in pixels, to leave above and below the image.

Methods

Inherits properties from its parent, HTMLElement.

HTMLImageElement.decode()

Returns a Promise that resolves when the image is decoded and it's safe to append the image to the DOM. This prevents rendering of the next frame from having to pause to decode the image, as would happen if an undecoded image were added to the DOM.

Errors

If an error occurs while trying to load or render the image, and an onerror event handler has been configured to handle the error event, that event handler will get called. This can happen in a number of situations, including:

• The src attribute is empty or null.
• The specified src URL is the same as the URL of the page the user is currently on.
• The specified image is corrupted in some way that prevents it from being loaded.
• The specified image's metadata is corrupted in such a way that it's impossible to retrieve its dimensions, and no dimensions were specified in the <img> element's attributes.
• The specified image is in a format not supported by the user agent.

Example

var img1 = new Image(); // Image constructor
img1.src = 'image1.png';
img1.alt = 'alt';
document.body.appendChild(img1);

var img2 = document.createElement('img'); // Use DOM HTMLImageElement
img2.src = 'image2.jpg';
img2.alt = 'alt text';
document.body.appendChild(img2);

// using first image in the document
alert(document.images[0].src);

Specifications

Browser compatibility

BCD tables only load in the browser

See also

• The HTML element implementing this interface: <img>