JavaScript Trick: Exclamation Before Function

By Xah Lee. Date: . Last updated: .

What does exclamation/bang symbol before function mean?

!function(…){…}(…);

What does that !function mean?

It is equivalent to this:

(function(…){…})(…);

It means, define a function expression, and evaluate it right there.

The exclamation is the boolean “not” operator. [see JS: true, false]

The exclamation forces what follows into a expression.

People do this hack to save one character worth of source code file size.

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JavaScript in Depth

Basics

  1. JavaScript Basics
  2. true, false
  3. Operators
  4. Branch Control
  5. Loop
  6. Array Basics
  7. Object Basics
  8. RegExp Basics

Variable

  1. Value Types
  2. let ⭐
  3. const ⭐
  4. var
  5. var Order
  6. var Scope
  7. Global Variable
  8. Destructuring Assignment ⭐

String

  1. String Overview
  2. Template String ⭐
  3. Char, Code Unit, Codepoint
  4. String Escape Sequence
  5. Unicode Escape Sequence

Function

  1. Define Function
  2. Arrow Function ⭐
  3. Function Params
  4. “arguments” Object
  5. Rest Params ⭐
  6. Arg Default Value ⭐
  7. Arg Destructure ⭐
  8. f Declaration vs Expression
  9. Closure
  10. f call apply bind
  11. Functional Programing

Object Property

  1. Property Overview
  2. Property Key
  3. Dot vs Bracket Notation
  4. Create/Delete Property
  5. Get/Set Property
  6. Check Property Existence
  7. Access Property
  8. List Properties
  9. Property Attributes
  10. Getter/Setter
  11. Property Descriptor
  12. Symbol

Object and Inheritance

  1. Object Overview
  2. Object Type
  3. Find Object's Type
  4. Prototype Chain
  5. Create Object
  6. Object Literal Expr
  7. Create Object with Parent X
  8. Get/Set Parent
  9. Show Prototype Chain
  10. Prevent Adding Property
  11. Clone Object
  12. Test Object Equality
  13. Add Method to Prototype

Array

  1. Understand JS Array
  2. Create Array
  3. Sparse Array
  4. Array-Like Object
  5. Array How-To

Class

  1. “this” Binding
  2. What's Constructor?
  3. Property Key "prototype"
  4. Operator “new”
  5. Operator “instanceof”
  6. Property Key “constructor”
  7. Class ⭐
  8. Keyword “extends” ⭐
  9. Keyword “super” ⭐

Iterable ⭐

  1. Interface
  2. Iterable
  3. Iterator
  4. Iterator Prototype
  5. for-of Loop
  6. Spread Operator
  7. Generator
  8. Generator Function

Misc

  1. Set Object ⭐
  2. Map Object ⭐
  3. Try Catch Throw Finally
  4. Import/Export ⭐
  5. Promise ⭐
  6. Proxy ⭐
  7. ES2015 Features
  8. How to Convert ES5 to ES2015
  9. Style Guide
  10. Semicolon Rules
  11. Exclamation Before Function
  12. How to Determine Strict Mode?
  13. x.y.z Associativity
  14. Function Chain
  15. Random Number, Range, Integer, Element
  16. Timing JS Code
  17. Range Function for Array
  18. Random Array Element, Randomize Array
  19. Tagged Template String
  20. String to Number
  21. Format Number

Object Reference

  1. the Global Object
  2. Object 🙼 Object.prototype
  3. Array 🙼 Array.prototype
  4. Function 🙼 Function.prototype
  5. String 🙼 String.prototype
  6. RegExp 🙼 RegExp.prototype 🙼 RegExp Syntax
  7. Date 🙼 Date.prototype
  8. Set ⭐🙼 Set.prototype
  9. Map ⭐🙼 Map.prototype
  10. JSON
  11. Math
  12. Reflect ⭐
  13. Symbol ⭐🙼 Symbol.prototype
  14. Number 🙼 Number.prototype
  15. Boolean 🙼 Boolean.prototype

DOM How-To

  1. Basic DOM Methods
  2. Get Elements by ID, Tag, Name, Class, CSS Selector
  3. Change CSS
  4. Change Node Content
  5. Create/Insert Node
  6. Remove Node
  7. Get Element's Attribute Value
  8. Set Element's Attribute Value
  9. Remove Element's Attribute Value
  10. List/Add/Remove Class Attribute
  11. Add/Remove Event Handler
  12. Navigate DOM Tree

DOM Overview

  1. Browser Window Object, Document Object Model
  2. Intro to Event-Based Programing
  3. JavaScript Load Order
  4. What is Live Object
  5. NodeList vs HTMLCollection
  6. DOM: Whitespace Nodes

Basic DOM Methods

  1. Basic DOM Methods
  2. Node Type, Name, Value
  3. Navigate DOM Tree

HTML Form

  1. HTML Form
  2. Visit URL in a New Window
  3. Instant Field Validation
  4. Input Field Validation
  5. HTML: Input Range Slider

DOM How To

  1. Encode URL, Escape String
  2. Browser Info, Navigator Object
  3. Get URL (window.location)
  4. Web Cookies
  5. Web Storage
  6. Find Window Width
  7. Find Element Width
  8. WebSocket

Web Scripting Examples

  1. Disable Right Click
  2. document.write
  3. Image Rollover
  4. Pop-up New Window
  5. Digital Clock
  6. Stopwatch
  7. Fade a Element
  8. Fade a Element Using CSS Transition
  9. Shake Element
  10. How to Create Tooltip
  11. Falling Snow Effect
  12. JavaScript: Floating Box Following Scroll

DOM Misc

  1. Value of “this” in Event Handler
  2. Event Delegation
  3. Get Current Script Tag
  4. insertAfter Element
  5. Randomize List
  6. create Document Fragment
  7. innerHTML, nodeValue, textContent, innerText?

jQuery

  1. jQuery Basics
  2. jQuery() vs querySelectorAll()
  3. Write JQuery Plugin

node.js