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Introduction to the use of setCapture and releaseCapture in HTML_javascript skills
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2016-05-16 17:55:001218browse
In addition, another very important thing is that on Win32, the mouse move event is not continuous. That is to say, not every time we move the 1px mouse pointer, a mousemove will occur. Windows will check periodically. The mouse position changes to generate the mousemove event. So, if it is a small page object, such as a dot with a diameter of 5px, if there is no setCapture and releaseCapture, then after pressing and holding the mouse, if you move the mouse quickly, it is possible that the mouse will move away, but the small The dot is still in place because the next mousemove event is no longer sent to the dot object.
The biggest difference between web development and windows development is that windows development is stateful, while web development is stateless. In windows, all operations can be controlled by the program, unless ctrl alt del is forced; But web operations are different. Even if a very important operation is performed, as soon as the user clicks the browser close button, the results of the previous operation will be wiped out. Although some code can be added to the onunload event to allow the user to choose whether to exit, but It cannot fundamentally solve the problem!
A few days ago, I saw the setCapture method from the Internet and learned about it. It roughly means this. When this method is used in a certain area of the IE document, and writes Onclick or onmouse*** and other related mouse event methods, then it will monitor the corresponding mouse operation. Even if your mouse moves out of IE, it can still capture it. If you write in the onclick event in a certain div An alert command. At this time, when you click the close button, it will also pop up the alert window. releaseCapture is the opposite of the setCapture method, releasing the mouse monitor.
Using this feature, we can delay IE's closing of the window and other damage Destructive operations, some important operations can be processed before destructive operations are performed. It is a pity: setCapture and releaseCapture do not support keyboard events. Only onmousedown, onmouseup, onmousemove, onclick, ondblclick, onmouseover, onmouseout and so on Mouse events work.
The following is a small example, if we want to protect the content in the div element divMain: 1. Execute the setCapture method on divMain: document.getElementById(" divMain").setCapture(); 2. Add a button btnChange to switch between setCapture and releaseCapture, and define a global variable; var isFreeze = true; 3. In the onclick event of btnChange, Add the following code:
Click Look at the IE menu or button :) or outside the IE window id="btnChange"> ;
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About the application of call and apply functions in javascript We often encounter call and apply functions in object-oriented applications in javascript; Sometimes you get confused. In fact, they can change the value of this reserved word in a function or object; the default value of this reserved word is the class itself. For example:
You will understand quickly after running the above page. The call and apply functions can handle anonymous functions The initialization application of the class is as follows:
The call and apply functions can assign function content (with anonymous parameters; but not triggered) The application of function binding events is as follows:
Function.prototype.Bind = function() { var __m = this, object = arguments[0], args = new Array(); for(var i = 1; i < ; arguments.length; i ){ args.push(arguments[i]); } return function() { return __m.apply(object, args); } }
The function functions of call and apply are the same; only the parameter formats are different; fun.call(obj, arguments); the arguments of apply are in array form; call is in singular form.
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