Determining creation date of an image in Javascript?_问答_开发者

Determining creation date of an image in Javascript?

开发者 https://www.devze.com 2023-01-20 01:14 出处：网络

I\'m attempting to create a page that displays and refreshes an image from a webcam (camimg.jpg), but displays a static image (notlive.jpg) if the image hasn\'t been updated recently. I\'ve found the

I'm attempting to create a page that displays and refreshes an image from a webcam (camimg.jpg), but displays a static image (notlive.jpg) if the image hasn't been updated recently. I've found the AJAXCam script, which serves the purpose of reloading the "live" image at a set interval (15 secs), yet with no Javascript experience I can't figure out how to determine when the image was last updated in order to decide whether or not camimg.jpg or notlive.jpg should be displayed.

My limited experience with programming has me thinking it should be something along the lines of:

pageLoaded = time page loaded in browser
imageUpdated = time the image was uploaded to server

if imageUpdated is not within 20 seconds of pageLoaded:
    display notlive.jpg
else:
    run AJAXCam

The AJAXCam code (initially called by <body onLoad="holdUp()">) is as follows:

<script type="text/javascript">
<开发者_Go百科!--
//
//AJAXCam v0.8b (c) 2005 Douglas Turecek http://www.ajaxcam.com
//
function holdUp()
{
//
// This function is first called either by an onLoad event in the <body> tag
// or some other event, like onClick.
//
// Set the value of refreshFreq to how often (in seconds)
// you want the picture to refresh
//
refreshFreq=15;
//
//after the refresh time elapses, go and update the picture
//
setTimeout("freshPic()", refreshFreq*1000);
}

function freshPic()
{
//
// Get the source value for the picture
// e.g. http://www.mysite.com/doug.jpg and
//
var currentPath=document.campic.src;
//
// Declare a new array to put the trimmed part of the source
// value in
//
var trimmedPath=new Array();
//
// Take everything before a question mark in the source value
// and put it in the array we created e.g. doug.jpg?0.32234 becomes
// doug.jpg (with the 0.32234 going into the second array spot
//
trimmedPath=currentPath.split("?");
//
// Take the source value and tack a qustion mark followed by a random number
// This makes the browser treat it as a new image and not use the cached copy
//
document.campic.src = trimmedPath[0] + "?" + Math.random();
//
// Go back and wait again.
holdUp();
}

// -->
</script>

Is what I'm trying to accomplish even possible? And if so, how would I go about implementing it? Thanks in advance for the help!

There is no way to do it in javascript.

Your only option is, in case you have access to server side languages like PHP you can send a simple HEAD request and check Last Modified header of the image then report it back to the browser via Ajax.