Immediately invoked function expression
An immediately invoked function expression is a JavaScript function expression that is defined and executed immediately within the same syntactic construct, often creating an isolated scope.
Secrets of the JavaScript Ninja, Second Edition
A function expression that is defined and invoked immediately in the same syntactic construct.
- How it is used
- Uses immediate invocation to run one-time work and give pre-ES6 modules a scope for hidden variables.
- How deep it goes
- Explains call-expression syntax, then works through scoped state, closures, and an object-based module interface.
- Examples
- Shows immediate-call syntax, a click-counting module, and a DOM dimension utility that hides temporary style settings.
- What you can do after
- Build it from scratch to run setup immediately while keeping state private and exposing selected functionality.
Functional Programming in JavaScript
An immediately invoked function expression is a function expression that is executed as soon as it is defined, typically to create an isolated scope.
- How it is used
- Uses immediate execution to create module boundaries that hide implementation details and limit globally shared data.
- How deep it goes
- Explains function scope, closures, private variables, and exported methods, but defers detailed variations of module patterns.
- Examples
- Demonstrates a MyModule skeleton whose private variables support exported methods through a closure.
- What you can do after
- Apply it via JavaScript function expressions to encapsulate module state and expose selected functionality.
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The Joy of JavaScript
A function expression that is defined and executed immediately, often to create a private scope and avoid leaking bindings.
- How it is used
- Provides encapsulated namespaces, legacy modularity, and immediate startup execution without requiring a module system.
- How deep it goes
- Explains function-scope encapsulation, namespace exposure, mixin context, and async invocation, while deferring detailed module internals.
- Examples
- Uses a Transaction namespace, a HasHash mixin, and dynamic-import initialization as concrete applications.
- What you can do after
- Build encapsulated namespaces and mixins, or start asynchronous initialization through an immediately invoked async function.
Read how The Joy of JavaScript explains immediately invoked function expression →
Related concepts
- function expressionkind of · A function expression is an expression that creates a function value, which can be assigned, passed, or used within another expression.
- module patternused by · The module pattern is a software design pattern that encapsulates implementation details and state while exposing a controlled public interface.
- scopeproduces · Scope is the region of a program in which names are visible and can be resolved according to the language’s lookup rules.
- modulealternative to · A module is a distinct, bounded software unit that groups related code or functionality and provides an organizational or interaction boundary within a larger system.
- modularityused by · Modularity is the property of a system being organized into separable components with distinct responsibilities and defined interactions.
- encapsulationaddresses · Encapsulation is a software design principle that contains state and implementation details behind a controlled interface, limiting direct access from outside.
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