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POError in IE when manually calling event handler, given certain conditions
 

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  1. POError in IE when manually calling event handler, given certain conditions
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    <h2>Preface</h2> <ul> <li>Please note, I'm not looking for a code solution, but rather insight into why this may occur.</li> <li>The error occurs in IE (tested 7 &amp; 8), but not Firefox, Chrome, Safari.</li> </ul> <h2>Description</h2> <p>When manually calling a function assigned to <code>onclick</code>, IE with throw a <code>Error: Object doesn't support this action</code> if <em>all of the following conditions</em> are met:</p> <ol> <li>You call the method directly via the element's <code>on[event]</code> property.</li> <li>You do not use <code>.call()</code> or <code>.apply()</code>.</li> <li>You pass an argument (any argument, even <code>undefined</code>).</li> <li>You attempt to assign the return value to a variable.</li> </ol> <p>Violate any one of those rules, and the call succeeds.</p> <p>The function itself appears to have nothing to do with it. An empty function gives the same result.</p> <h2>Code</h2> <pre><code>var elem = document.getElementById('test'); // simple div element. var result; // store result returned. function test_func(){}; // function declaration. // function expression behaves identically. elem.onclick = test_func; // assign test_func to element's onclick. // DIRECT CALL test_func(); // works test_func( true ); // works result = test_func(); // works result = test_func( true ); // works // DIRECT CALL, CHANGING THE CONTEXT TO THE ELEMENT test_func.call( elem ); // works test_func.call( elem, true ); // works result = test_func.call( elem ); // works result = test_func.call( elem, true ); // works ******** (surprising) // CALL VIA ELEMENT, USING .call() METHOD, CHANGING THE CONTEXT TO THE ELEMENT elem.onclick.call( elem ); // works elem.onclick.call( elem, true ); // works result = elem.onclick.call( elem ); // works result = elem.onclick.call( elem, true ); // works ******** ( very surprising) // CALL VIA ELEMENT elem.onclick(); // works elem.onclick( true ); // works result = elem.onclick(); // works result = elem.onclick( true ); // Error: Object doesn't support this action </code></pre> <h2>Summary</h2> <p>Again, I don't need a code solution. Rather I'm curious if anyone has insight into why IE is implemented this way.</p> <p>Many thanks.</p> <hr> <p><strong>EDIT:</strong> To clarify one thing, nothing with the actual function seems to make any difference. Naming parameters, not naming them, returning the argument, returning a literal value, returning undefined, all of these have no effect.</p> <p>This is likely because the function seems to never actually get called. As I noted in a comment below, the code leading up to this call runs fine, so it isn't a parsing issue either. But when the interpreter gets to this one, it sees:</p> <blockquote> <p>Variable + AssignmentOperator + DOMElement + EventHandler + CallOperator + Argument</p> </blockquote> <p>...and throws the Error. No manipulation I do seems to make any difference. A valid removal of any one of those, and the Error disappears.</p> <p>If I place add a variable to the middle of it that stores the handler, then fire it from the variable it works.</p> <pre><code>var temp = elem.onclick; result = temp( true ); // works </code></pre> <p>...but this shouldn't be much of a surprise, since it is effectively the same as the fourth version above.</p>
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    1. COCan you elaborate on your "surprising" and "very surprising" annotations? To me, none of them are surprising. The last snippet surprises me, though. Assigning the return value of a function to a variable should not yield "doesn't support this action".
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    2. CO@August Lilleaas - Surprising only when you compare them to the one that receives the `Error:`, since like that one, they are called from the context of the element, are passing an argument, and are assigning the return value. Otherwise, not surprising at all.
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    3. COHaven't got an idea yet about the other conditions, but clearly .apply and .call create a new copy of the function. That's why it works in that case.
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