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copied!<p>A <em>closure</em> is much like an object. It gets instantiated whenever you call a function. </p> <p>The scope of a <em>closure</em> in JavaScript is lexical, which means that everything that is contained within the function the <em>closure</em> belongs to, has access to any variable that is in it.</p> <p>A variable is contained in the <em>closure</em> if you</p> <ol> <li>assign it with <code>var foo=1;</code> or</li> <li>just write <code>var foo;</code></li> </ol> <p>If an inner function (a function contained inside another function) accesses such a variable without defining it in its own scope with var, it modifies the content of the variable in the outer <em>closure</em>.</p> <p>A <em>closure</em> outlives the runtime of the function that spawned it. If other functions make it out of the <em>closure/scope</em> in which they are defined (for instance as return values), those will continue to reference that <em>closure</em>.</p> <h2>Example</h2> <pre><code> function example(closure) { // define somevariable to live in the closure of example var somevariable = 'unchanged'; return { change_to: function(value) { somevariable = value; }, log: function(value) { console.log('somevariable of closure %s is: %s', closure, somevariable); } } } closure_one = example('one'); closure_two = example('two'); closure_one.log(); closure_two.log(); closure_one.change_to('some new value'); closure_one.log(); closure_two.log(); </code></pre> <h2>Output</h2> <pre><code>somevariable of closure one is: unchanged somevariable of closure two is: unchanged somevariable of closure one is: some new value somevariable of closure two is: unchanged </code></pre>

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