Image

创建源

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

• onAbort
• onError
• onKeyDown
• onKeyPress
• onKeyUp
• onLoad

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

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

<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

属性

描述

示例

function checkBorder(theImage) {
   if (theImage.border==0) {
      alert('The image has no border!')
   }
   else alert('The image's border is ' + theImage.border)
}

参看

complete

示例

<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

height

描述

示例

function showImageSize(theImage) {
   alert('height=' + theImage.height+
      '; width=' + theImage.width +
      '; hspace=' + theImage.hspace +
      '; vspace=' + theImage.vspace)
}

参看

hspace

描述

示例

参看

lowsrc

描述

示例

参看

name

安全性

描述

示例

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

src

描述

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

<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

vspace

描述

示例

参看

width

描述

示例

参看

方法

语法

描述