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copied!<p>A GOOD way to declare a global variable in Javascript would be <code>window.globalVariableName</code> rather than <code>var globalVariableName;</code> Or if you are not running your application in browser replace window with global object specific to that invironment.</p> <p>The first declaration will work no matter where you are in global scope or in a function. </p> <p>A BAD way to declare a global variable is </p> <pre><code>globalVariableName = 'Foo'; </code></pre> <p>Because it isn't an obvious declaration and looks a lot like just forgetting the var.</p> <p>And finally globalVariables is not a good thing to use. So use them thoughtfully. Try to check if they are not used already by another script say like that</p> <pre><code>if(window.globalVariableName === undefined) window.globalVariableName = 'Bar'; </code></pre> <p>Try reading first chapter of JavaScript Patterns Stoyan Stefanov for more explanation.</p> <p>UPDATE: awsering Andreas Rossberg</p> <p>For example David Flanigan in Definitive Javascript Guide states in 4.6.1 what are global variables, they are properties of the global object. You can confirm this on MDN also. </p> <p>About bad style, i can agree but only partially, because if you don't use the <em>Single var Pattern</em> for variable declarations like this </p> <pre><code>(function(){ var someVar1 = '', someVar2 = null, someVar3 = undefined; })(); </code></pre> <p>your code will look just as bad. </p> <p>As to next version of EcmaScript again you are a little too brief on reference. I've read only that <code>this</code> will be handled differently in strict Javascript. If I understood you correctly this example is what you are referring to </p> <pre><code>function someFunction() { //'use strict'; console.log(this); //Window or undefined console.log(window);// Window or Window } someFunction(); </code></pre> <p>Uncommenting 'use strict'; will give undefined for this in first log, but still Window for the second log.</p>

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