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Image
An image on an HTML form.
创建源
The Image constructor or the IMG tag.
The JavaScript runtime engine creates an Image object corresponding to each IMG tag in your document. It puts these objects in an array in the document.images property. You access an Image object by indexing this array.
To define an image with the IMG tag, use standard HTML语法 with the addition of JavaScript event handlers. If specify a value for the NAME attribute, you can use that name when indexing the images array.
To define an image with its constructor, use the following语法:
new Image(width, height)
参数
事件句柄
To define an事件适用对象an Image object created with the Image constructor, set the appropriate property of the object. For example, if you have an Image object named imageName and you want to set one of its event handlers to a function whose name is handlerFunction, use one of the following statements:
imageName.onabort = handlerFunction
imageName.onerror = handlerFunction
imageName.onkeydown = handlerFunction
imageName.onkeypress = handlerFunction
imageName.onkeyup = handlerFunction
imageName.onload = handlerFunction
Image objects do not have onClick, onMouseOut, and onMouseOver event handlers. However, if you define an Area object for the image or place the IMG tag within a Link object, you can use the Area or Link object's event handlers. See Link.
描述
The position and size of an image in a document are set when the document is displayed in the web browser and cannot be changed using JavaScript (the width and height properties are read-only for these objects). You can change which image is displayed by setting the src and lowsrc properties. (See the描述s of Image.src and Image.lowsrc.)
You can use JavaScript to create an animation with an Image object by repeatedly setting the src property, as shown in Example 4 below. JavaScript animation is slower than GIF animation, because with GIF animation the entire animation is in one file; with JavaScript animation, each frame is in a separate file, and each file must be loaded across the network (host contacted and data transferred).
The primary use for an Image object created with the Image constructor is to load an image from the network (and decode it) before it is actually needed for display. Then when you need to display the image within an existing image cell, you can set the src property of the displayed image to the same value as that used for the previously fetched image, as follows.
myImage = new Image()
myImage.src = "seaotter.gif"
...
document.images[0].src = myImage.src
The resulting image will be obtained from cache, rather than loaded over the network, assuming that sufficient time has elapsed to load and decode the entire image. You can use this technique to create smooth animations, or you could display one of several images based on form input.
属性概览
方法概览
示例
示例 1: Create an image with the IMG tag. The following code defines an image using the IMG tag:
<IMG NAME="aircraft" SRC="f15e.gif" ALIGN="left" VSPACE="10">
The following code refers to the image:
document.aircraft.src='f15e.gif'
When you refer to an image by its name, you must include the form name if the image is on a form. The following code refers to the image if it is on a form:
document.myForm.aircraft.src='f15e.gif'
示例 2: Create an image with the Image constructor. The following example creates an Image object, myImage, that is 70 pixels wide and 50 pixels high. If the source URL, seaotter.gif, does not have dimensions of 70x50 pixels, it is scaled to that size.
myImage = new Image(70, 50)
myImage.src = "seaotter.gif"
If you omit the width and height arguments from the Image constructor, myImage is created with dimensions equal to that of the image named in the source URL.
myImage = new Image()
myImage.src = "seaotter.gif"
示例 3: Display an image based on form input. In the following example, the user selects which image is displayed. The user orders a shirt by filling out a form. The image displayed depends on the shirt color and size that the user chooses. All possible image choices are preloaded to speed response time. When the user clicks the button to order the shirt, the allShirts function displays the images of all the shirts.
<SCRIPT>
shirts = new Array()
shirts[0] = "R-S"
shirts[1] = "R-M"
shirts[2] = "R-L"
shirts[3] = "W-S"
shirts[4] = "W-M"
shirts[5] = "W-L"
shirts[6] = "B-S"
shirts[7] = "B-M"
shirts[8] = "B-L"
doneThis = 0
shirtImg = new Array()
// Preload shirt images
for(idx=0; idx < 9; idx++) {
shirtImg[idx] = new Image()
shirtImg[idx].src = "shirt-" + shirts[idx] + ".gif"
}
function changeShirt(form)
{
shirtColor = form.color.options[form.color.selectedIndex].text
shirtSize = form.size.options[form.size.selectedIndex].text
newSrc = "shirt-" + shirtColor.charAt(0) + "-" + shirtSize.charAt(0) + ".gif"
document.shirt.src = newSrc
}
function allShirts()
{
document.shirt.src = shirtImg[doneThis].src
doneThis++
if(doneThis != 9)setTimeout("allShirts()", 500)
else doneThis = 0
return
}
</SCRIPT>
<FONT SIZE=+2><B>Netscape Polo Shirts!</FONT></B>
<表 CELLSPACING=20 BORDER=0>
<TR>
<TD><IMG name="shirt" SRC="shirt-W-L.gif"></TD>
<TD>
<FORM>
<B>Color</B>
<SELECT SIZE=3 NAME="color" onChange="changeShirt(this.form)">
<OPTION> Red
<OPTION SELECTED> White
<OPTION> Blue
</SELECT>
<P>
<B>Size</B>
<SELECT SIZE=3 NAME="size" onChange="changeShirt(this.form)">
<OPTION> Small
<OPTION> Medium
<OPTION SELECTED> Large
</SELECT>
<P><INPUT type="button" name="buy" value="Buy This Shirt!"
onClick="allShirts()">
</FORM>
</TD>
</TR>
</表>
示例 4: JavaScript animation. The following example uses JavaScript to create an animation with an Image object by repeatedly changing the value the src property. The script begins by preloading the 10 images that make up the animation (image1.gif, image2.gif, image3.gif, and so on). When the Image object is placed on the document with the IMG tag, image1.gif is displayed and the onLoad event handler starts the animation by calling the animate function. Notice that the animate function does not call itself after changing the src property of the Image object. This is because when the src property changes, the image's onLoad event handler is triggered and the animate function is called.
<SCRIPT>
delay = 100
imageNum = 1
// Preload animation images
theImages = new Array()
for(i = 1; i < 11; i++) {
theImages[i] = new Image()
theImages[i].src = "image" + i + ".gif"
}
function animate() {
document.animation.src = theImages[imageNum].src
imageNum++
if(imageNum > 10) {
imageNum = 1
}
}
function slower() {
delay+=10
if(delay > 4000) delay = 4000
}
function faster() {
delay-=10
if(delay < 0) delay = 0
}
</SCRIPT>
<BODY BGCOLOR="white">
<IMG NAME="animation" SRC="image1.gif" ALT="[Animation]"
onLoad="setTimeout('animate()', delay)">
<FORM>
<INPUT TYPE="button" Value="Slower" onClick="slower()">
<INPUT TYPE="button" Value="Faster" onClick="faster()">
</FORM>
</BODY>
See also the示例 for the onAbort, onError, and onLoad event handlers.
参看
Link, onClick, onMouseOut, onMouseOver
属性
border
A string specifying the width, in pixels, of an image border.
描述
The border property reflects the BORDER attribute of the IMG tag. For images created with the Image constructor, the value of the border property is 0.
示例
The following function displays the value of an image's border property if the value is not 0.
function checkBorder(theImage) {
if (theImage.border==0) {
alert('The image has no border!')
}
else alert('The image's border is ' + theImage.border)
}
参看
Image.height, Image.hspace, Image.vspace, Image.width
complete
A boolean value that indicates whether the web browser has completed its attempt to load an image.
示例
The following example displays an image and three radio buttons. The user can click the radio buttons to choose which image is displayed. Clicking another button lets the user see the current value of the complete property.
<B>Choose an image:</B>
<BR><INPUT TYPE="radio" NAME="imageChoice" VALUE="image1" CHECKED
onClick="document.images[0].src='f15e.gif'">F-15 Eagle
<BR><INPUT TYPE="radio" NAME="imageChoice" VALUE="image2"
onClick="document.images[0].src='f15e2.gif'">F-15 Eagle 2
<BR><INPUT TYPE="radio" NAME="imageChoice" VALUE="image3"
onClick="document.images[0].src='ah64.gif'">AH-64 Apache
<BR><INPUT TYPE="button" VALUE="Is the image completely loaded?"
onClick="alert('The value of the complete property is '
+ document.images[0].complete)">
<BR>
<IMG NAME="aircraft" SRC="f15e.gif" ALIGN="left" VSPACE="10"><BR>
参看
Image.lowsrc, Image.src
height
A string specifying the height of an image in pixels.
描述
The height property reflects the HEIGHT attribute of the IMG tag. For images created with the Image constructor, the value of the height property is the actual, not the displayed, height of the image.
示例
The following function displays the values of an image's height, width, hspace, and vspace properties.
function showImageSize(theImage) {
alert('height=' + theImage.height+
'; width=' + theImage.width +
'; hspace=' + theImage.hspace +
'; vspace=' + theImage.vspace)
}
参看
Image.border, Image.hspace, Image.vspace, Image.width
hspace
A string specifying a margin in pixels between the left and right edges of an image and the surrounding text.
描述
The hspace property reflects the HSPACE attribute of the IMG tag. For images created with the Image constructor, the value of the hspace property is 0.
示例
See the示例 for the height property.
参看
Image.border, Image.height, Image.vspace, Image.width
lowsrc
A string specifying the URL of a low-resolution version of an image to be displayed in a document.
描述
The lowsrc property initially reflects the LOWSRC attribute of the IMG tag. The web browser loads the smaller image specified by lowsrc and then replaces it with the larger image specified by the src property. You can change the lowsrc property at any time.
示例
See the示例 for the src property.
参看
Image.complete, Image.src
name
A string specifying the name of an object.
安全性
Navigator 3.0：该属性默认是带有污点的。有关数据污点的更多信息，请看“JavaScript 的安全性”。
描述
Represents the value of the NAME attribute. For images created with the Image constructor, the value of the name property is null.
示例
In the following example, the valueGetter function uses a for loop to iterate over the array of elements on the valueTest form. The msgWindow window displays the names of all the elements on the form:
newWindow=window.open("http://home.netscape.com")
function valueGetter() {
var msgWindow=window.open("")
for (var i = 0; i < newWindow.document.valueTest.elements.length; i++) {
msgWindow.document.write(newWindow.document.valueTest.elements[i].name + "<BR>")
}
}
In the following example, the first statement creates a window called netscapeWin. The second statement displays the value "netscapeHomePage" in the Alert dialog box, because "netscapeHomePage" is the value of the windowName argument of netscapeWin.
netscapeWin=window.open("http://home.netscape.com","netscapeHomePage")
alert(netscapeWin.name)
prototype
Represents the prototype for this class. You can use the prototype to add properties or methods to all instances of a class. For more information, see Function.prototype.
src
A string specifying the URL of an image to be displayed in a document.
描述
The src property initially reflects the SRC attribute of the IMG tag. Setting the src property begins loading the new URL into the image area (and aborts the transfer of any image data that is already loading into the same area). Therefore, if you plan to alter the lowsrc property, you should do so before setting the src property.
If the URL in the src property refers to an image that is not the same size as the image cell it is loaded into, the source image is scaled to fit.
When you change the src property of a displayed image, the new image you specify is displayed in the area defined for the original image. For example, suppose an Image object originally displays the file beluga.gif:
<IMG NAME="myImage" SRC="beluga.gif" ALIGN="left">
If you set myImage.src='seaotter.gif', the image seaotter.gif is scaled to fit in the same space originally used by beluga.gif, even if seaotter.gif is not the same size as beluga.gif.
You can change the src property at any time.
示例
The following example displays an image and three radio buttons. The user can click the radio buttons to choose which image is displayed. Each image also uses the lowsrc property to display a low-resolution image.
<SCRIPT>
function displayImage(lowRes,highRes) {
document.images[0].lowsrc=lowRes
document.images[0].src=highRes
}
</SCRIPT>
<FORM NAME="imageForm">
<B>Choose an image:</B>
<BR><INPUT TYPE="radio" NAME="imageChoice" VALUE="image1" CHECKED
onClick="displayImage('f15el.gif','f15e.gif')">F-15 Eagle
<BR><INPUT TYPE="radio" NAME="imageChoice" VALUE="image2"
onClick="displayImage('f15e2l.gif','f15e2.gif')">F-15 Eagle 2
<BR><INPUT TYPE="radio" NAME="imageChoice" VALUE="image3"
onClick="displayImage('ah64l.gif','ah64.gif')">AH-64 Apache
<BR>
<IMG NAME="aircraft" SRC="f15e.gif" LOWSRC="f15el.gif" ALIGN="left" VSPACE="10"><BR>
</FORM>
参看
Image.complete, Image.lowsrc
vspace
A string specifying a margin in pixels between the top and bottom edges of an image and the surrounding text.
描述
The vspace property reflects the VSPACE attribute of the IMG tag. For images created with the Image constructor, the value of the vspace property is 0.
示例
See the示例 for the height property.
参看
Image.border, Image.height, Image.hspace, Image.width
width
A string specifying the width of an image in pixels.
描述
The width property reflects the WIDTH attribute of the IMG tag. For images created with the Image constructor, the value of the width property is the actual, not the displayed, width of the image.
示例
See the示例 for the height property.
参看
Image.border, Image.height, Image.hspace, Image.vspace
方法
handleEvent
调用指定事件的控制句柄。
语法
handleEvent(event)
参数
描述
要获得关于事件句柄的更多信息，请看“关于事件的常规信息”。
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