An '''immediately invoked function expression''' (or '''IIFE''', pronounced "iffy")<ref name="Alman">{{cite web |last=Alman |first=Ben |title=Immediately Invoked Function Expressions |url=http://benalman.com/news/2010/11/immediately-invoked-function-expression/|title=Immediately Invoked Function Expressions|last=Alman|first=Ben|date=15 November 2010|accessdatewebsite=18 January 2019 |url-status=live|archive-url=https://web.archive.org/web/20171201033208/http://benalman.com/news/2010/11/immediately-invoked-function-expression/|archive-date=1 December 2017|url-statusaccessdate=live18 January 2019}}</ref> is a [[JavaScript]] [[Programming idiom|programming language idiom]] which produces a [[scope (computer science)|lexical scope]] using JavaScript's [[function scoping]].
Immediately invoked function expressions can be used to avoid [[JavaScript syntax#Scoping and hoisting|variable hoisting]] from within blocks, protect against polluting the [[Global variable|global environment]] and simultaneously allow public access to methods while retaining privacy for variables defined within the function.
