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    <p>The specification is quite clear that any name defined a catch statement will do nothing more than shadow a surrounding name. Beyond that I would not consider these errors as nothing more than a warning. Just using pure intuition I believe that this is simply overzealous analysis on the part of the designer of those Lint tools. </p> <p>Since a catch block introduces a new scope, using the same name will simply shadow any similar names in the enclosing scope. This isn't necessarily a bad thing if you are aware of the semantics. If you are coding under the assumption that the enclosing <code>err</code> will be accessible than you'll need to change your assumptions.</p> <p><strong>Specification</strong></p> <p>The production Catch : catch ( Identifier ) Block is evaluated as follows:</p> <ol> <li>Let C be the parameter that has been passed to this production.</li> <li>Let oldEnv be the running execution context’s LexicalEnvironment.</li> <li>Let catchEnv be the result of calling NewDeclarativeEnvironment passing oldEnv as the argument.</li> <li>Call the CreateMutableBinding concrete method of catchEnv passing the Identifier String value as the argument.</li> <li>Call the SetMutableBinding concrete method of catchEnv passing the Identifier, C, and false as arguments. Note that the last argument is immaterial in this situation.</li> <li>Set the running execution context’s LexicalEnvironment to catchEnv.</li> <li>Let B be the result of evaluating Block.</li> <li>Set the running execution context’s LexicalEnvironment to oldEnv.</li> <li>Return B.</li> </ol> <p><strong>NOTE</strong> No matter how control leaves the Block the LexicalEnvironment is always restored to its former state.</p>
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    1. POJavaScript catch parameter already defined
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    1. COThe second code block was merely a test to see if that would help or hurt the problem. (It hurt.) JSLint is trying to tell me something or steer away from somewhere that I could hurt myself, I want to know what that is -- not ignore warnings. The actual code would not have a local variable.
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      1. USWalt Stoneburner
    2. CODo you have a reference that catch blocks definitively introduce a new scope? Not doubting you, just want to read up on it.
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    3. CO@JaredPar: Catch blocks don't introduce a new variable environment, in ES3 they simply introduce an object at the top of the scope chain, that has a property named like the catch identifier, and its value is the exception that has been raised, in ES5 they introduce a LexicalEnvironment, but again not a "new scope" (variable and function declarations are always hoisted).
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