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Scope of variables in Javascript constructor, javascript Constructor
Constructor can be used with new to create objects. It can also be called as a common function because it is also a function.
function Person(name) {this.name=name;}Person(12);alert(window.name);//12
This indicates the global window object when the constructor is called as a common function. It is obvious that the constructor is treated as a common function call. It is not a good practice and there is no reason to do so. In practice, we should avoid such strange usage to avoid strange problems.
function Person(name,sex) { this.name=name; var name1="22"; name2=sex;}var per = new Person("aty","boy");alert(per.name);// atyalert(per.name1);//undefinedalert(per.name2);//undefinedalert(window.name2);//boy
The constructors define variables using this as member variables; var as local variables; without a keyword, this variable is added to the window object. This explains why the this keyword is used in constructors.
Function is not implemented,
However, your code is not a scope issue,
You set var targetImage = document. getElementById ('floatingimg ');
Put this sentence outside the floating method, that is, the page will be executed as soon as it is loaded, at this time, the id = "'floatingimg '" element has not been loaded (even the <body> element does not exist), of course, it is empty.
Put this code in window. onload = function () {};
A Javascript variable scope
Because in the second example, before you call test (), the sentence "document. write ("<LI>" + langVBS); "An error occurred (" langVBS undefined "). Therefore, the test () function is not called and only" document. write ("<LI>" + langJS.
In the first example, this error occurs only after test () is called, so the execution of the text () function is not affected.
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