Immediately invoked function expression: Difference between revisions

Revision as of 16:23, 2 May 2017

Revision as of 16:24, 2 May 2017

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Immediately-invoked function expressions may be written in a number of different ways.<ref name=Enlighten>{{cite book|last=Lindley|first=Cody|title=JavaScript Enlightenment|year=2013|publisher=O'Reilly|isbn=9781449342883|pages=61}}</ref> A [[Coding conventions|common convention]] is to enclose the function expression (and optionally its invocation operator) with the ''grouping operator'',<ref>{{cite web|url=https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Grouping|title=Grouping operator|publisher=Mozilla Developer Network}}</ref> i.e. in parentheses, to explicitly tell the parser to expect an expression. Otherwise, in most situations, when the parser encounters the <code>function</code> keyword, it treats it as a function declaration (statement), and not as a function expression.<ref>{{cite book|last=Zakas|first=Nicholas|title=Maintainable JavaScript|year=2012|publisher=O'Reilly|isbn=9781449327682|pages=44}}</ref>

<syntaxhighlight lang="JavaScript">

(function () { …/* ... */ })();

(function () { …/* ... */ }());

</syntaxhighlight>

There are other ways to enforce a function expression:

<syntaxhighlight lang="JavaScript">

!function () { …/* ... */ }();

~function () { …/* ... */ }();

-function () { …/* ... */ }();

+function () { …/* ... */ }();

void function () { …/* ... */ }();

</syntaxhighlight>

In contexts where an expression is expected, wrapping in parentheses is not necessary:

<syntaxhighlight lang="JavaScript">

var f = function () { …/* ... */ }();

true && function () { …/* ... */ }();

0, function () { …/* ... */ }();

</syntaxhighlight>

Passing variables into the scope is done as follows:

<syntaxhighlight lang="JavaScript">

(function(a, b) { …/* ... */ })("hello", "world");

</syntaxhighlight>

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})();

</syntaxhighlight>

…to avoid being parsed as <code>c(…)</code>.

==Examples==