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    <p>The solution is the binding of variables through closure.</p> <hr> <p>As a more basic example, here is an example function that receives and calls a callback function, as well as an example callback function:</p> <pre><code>function callbackReceiver(callback) { callback("Hello World"); } function callback(value1, value2) { console.log(value1, value2); } </code></pre> <p>This calls the callback and supplies a single argument. Now you want to supply an additional argument, so you wrap the callback in closure.</p> <pre><code>callbackReceiver(callback); // "Hello World", undefined callbackReceiver(function(value) { callback(value, "Foo Bar"); // "Hello World", "Foo Bar" }); </code></pre> <p>Or, more simply using <a href="https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Functions/Arrow_functions" rel="noreferrer">ES6 Arrow Functions</a>:</p> <pre><code>callbackReceiver(value =&gt; callback(value, "Foo Bar")); // "Hello World", "Foo Bar" </code></pre> <hr> <p>As for your specific example, I haven't used the <code>.post</code> function in jQuery, but a quick scan of the documentation suggests the call back should be a <i>function pointer</i> with the following signature:</p> <pre><code>function callBack(data, textStatus, jqXHR) {}; </code></pre> <p>Therefore I think the solution is as follows:</p> <pre><code>var doSomething = function(extraStuff) { return function(data, textStatus, jqXHR) { // do something with extraStuff }; }; var clicked = function() { var extraStuff = { myParam1: 'foo', myParam2: 'bar' }; // an object / whatever extra params you wish to pass. $.post("someurl.php", someData, doSomething(extraStuff), "json"); }; </code></pre> <p>What is happening?</p> <p>In the last line, <code>doSomething(extraStuff)</code> is <i>invoked</i> and the result of that invocation is a <i>function pointer</i>.</p> <p>Because <code>extraStuff</code> is passed as an argument to <code>doSomething</code> it is within scope of the <code>doSomething</code> function.</p> <p>When <code>extraStuff</code> is referenced in the returned anonymous inner function of <code>doSomething</code> it is bound by closure to the outer function's <code>extraStuff</code> argument. This is true even after <code>doSomething</code> has returned.</p> <p>I haven't tested the above, but I've written very similar code in the last 24 hours and it works as I've described.</p> <p>You can of course pass multiple variables instead of a single 'extraStuff' object depending on your personal preference/coding standards.</p>
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    1. POjQuery pass more parameters into callback
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    1. COWhat is the purpose of 'var doSomething = '? How is this different from just declaring doSomething as a function (ie function doSomething(...) {} )
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      1. USDave Neeley
    2. COIt isn't different really. "function foo() {};" is syntactic sugar for "var foo = function() {};". That said, I tend to prefer the var syntax especially when you're passing around the function as data.
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    3. COThat's not true. Different scope rules apply to these two function declarations. The behavior differs a lot depending on JS runtime (read browser). Also try to compare the function name shown in stacktrace/breakpoint in Firebug.
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      1. USIhor Kaharlichenko
 

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