onload | 易学教程

If I load multiple images with the for loop, do I only need one img.onload function?

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问题 So I am loading multiple images onto multiple canvases basically (one image per canvas/ctx - its a slideshow). I want to make sure that each image is loaded before it attempts to draw the image onto the canvas. Here is the code... In Example 1 i'm using 3 onload events (one for each image) In Example 2 i'm using one onload event, but it is the last image that gets called in the for loop Question: Can i use Example 2 and be confident to assume that if the last image is loaded, then the images

Want to call a function if iframe doesn't load or load's?

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问题 I have a iframe in my page. If the iframe doesn't load, want it to alert the message " pdf not found " and if the iframe does load, it should alert " pdf opened ". Does anyone know how to achieve that? 回答1: So, the idea is to use an Ajax-request to "test" the URL. Ajax-requests enable you to bind "success" and "error" handlers - unlike <iframe> elements which only provide a "load" handler. Of course, Ajax-requests are restricted by the Same Origin Policy (unless the web-server enables CORS),

Jquery .ready() vs window.onload [duplicate]

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问题 This question already has answers here : window.onload vs $(document).ready() (15 answers) Closed 5 years ago . Are there any advantages of using the Jquery ready() function over window.onload? // Jquery ready $(document).ready(function() { }); // window.onload window.onload = function () { } 回答1: Depends on what you want to do. jQuery ready will run your code when the HTML is all ready, but before images and other resources have finished. This is the earliest possible time that you can

Jquery .ready() vs window.onload [duplicate]

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Javascript multiple Dynamic Insertion

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问题 When we do dynamic insertion for javascript, sometimes order matters. We sometimes solve this by using onload property; however, if there are many external javascripts, and those scripts has to be loaded in order, then what should we do? I solved this problem by recursively defined onload functions; however not so sure about efficiency... since this is a script, I think it does lazy eval.... Any help? //recursively create external javascript loading chain //cautiously add url list according

Why not use javascript handlers on the body element?

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问题 As an answer to the question of 'How do you automatically set the focus to a textbox when a web page loads?', Espo suggests using <body onLoad="document.getElementById('<id>').focus();"> Ben Scheirman replies (without further explanation): Any javascript book will tell you not to put handlers on the body element like that Why would this be considered bad practice? In Espos answer, an 'override' problem is illustrated. Is this the only reason, or are there any other problems? Compatibility

substr() with negative value not working in IE

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问题 EDIT:I've changed the title, because the issue had nothing to do with IE image.load() firing - my substr() wasn't working (see accepted answer). There's a ton of posts about making sure that you define your onload handler prior to assigning img.src in order to guarantee that the onload handler is in place in case the image is loaded from cache first. This does not appear to the be issue in my code, since that's precisely what I have done. Note that this script works across all other browsers,

Is the 'onload' necessary when the code is at the bottom?

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问题 I was wondering if the window.onload = function(){} (or any other kind of onload, like the jQuery $(document).ready(); is necessary if the code is placed at the bottom of my <body> ? Or there could be highly unexpected side-effects? 回答1: Yes, there could be unexpected consequences. But, no, it's not absolutely necessary. The timing could be off for things still loading, like complicated layouts, deep DOM structures, dynamic HTML from other scripts, or images. To avoid these situations, it's

How to execute JavaScript after page load?

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问题 I would like to execute a JavaScript function after the page was loaded. At the moment I have a commandButton and everything works fine. However it would be more comfortable if the user is not supposed to hit the button. I have tried f:event, but I do not have a listener, I have only the JavaScript function. Moreover body onload does not work for me as I use only high level components. <f:view xmlns="http://www.w3.org/1999/xhtml" xmlns:f="http://java.sun.com/jsf/core" xmlns:p="http:/

How to trigger onload event when downloading a file in an iframe?

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问题 Suppose we have the following HTML file: <html xmlns="http://www.w3.org/1999/xhtml"> <head> <title>Test iframe download</title> <script type="text/javascript"> var init = 0; function download() { document.getElementById("dload_frame").src = "http://example.com/dload.py"; } function alert() { if (init == 0) { init = 1; } else { document.getElementById("alert_span").innerHTML = "Got it!"; } } </script> </head> <body> <span id="alert_span">Main content.</span><br/> <input type="button" value=