javascript检查图像是否存在 [英] javascript check image existence

问题描述

我正在尝试显示Google地图或图像.所以，我要的是默认情况下我要显示图像，如果图像不存在，请显示谷歌地图.为此，默认情况下，我使用#map_canvas {display:none;}禁用google maps.然后，我需要一个类似布尔条件的条件，该条件检查图像的存在，然后返回true或false，如果为false，则通过更改display ="block";显示地图.但是，我不能完全做到这一点，请您能帮助我吗?

I am trying to show either google map or image. So, what i want is that for default i want to show the image, if image does not exist, show google map. To do so, as a default I disable google maps with #map_canvas {display:none;}. Then, I need something like a boolean conditions that checks existence of image then, returns true or false, if it is false, display maps, by changing display="block";. But, I do not how to do that exactly, Can you please help me ?

顺便说一句，两个代码分别可以正常工作.

By the way, two codes separately work fine.

推荐答案

如果图像未加载到#worldMap中，则要显示#map_canvas，请使用

To show #map_canvas if the image does not load into #worldMap use

var img = document.getElementById("worldMap");
img.src = "http://www.freeworldmaps.net/download/maps/political-world-map-big.gif";

img.onerror = function( ) {
    img.style.display = "none";
    document.getElementById("map_canvas").style.display = "block";
}​​​​​​​​​​​​​​​​​

显然，您不必在img标签中指定src属性，而是在页面加载时将其设置为上面的值.

You obviously have to not specify the src attribute in your img tag but set it as above when the page loads.

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