Hoisting
Hoisting is JavaScript behavior in which certain declarations are registered within their scope before execution reaches their textual position.
Secrets of the JavaScript Ninja, Second Edition
A common description of JavaScript declaration handling as moving declarations to the top of a scope, although declarations are registered before code executes rather than literally moved.
- How it is used
- Clarifies identifier resolution by replacing the literal-movement shorthand with registration in lexical environments.
- How deep it goes
- Explains registration before execution and contrasts declaration forms, stopping short of further environment mechanics.
- Examples
- Compares early access to a function declaration with expressions and arrows, then shows a var assignment replacing a function.
- What you can do after
- Understand why declarations can be available before execution reaches them and why later assignments can change their values.
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The behavior by which declarations are processed as though moved to the top of their scope before execution, affecting when bindings can be accessed.
- How it is used
- Explains how declaration scope and access-before-declaration behavior distinguish `let` from `var`.
- How deep it goes
- Works through shadowing and temporal-dead-zone behavior, but does not delve into language implementation internals.
- Examples
- Uses shadowed `myData`, an early `let` read, and `var` versus `let` loop examples.
- What you can do after
- Understand when `let` and `var` bindings are in scope and what happens when code reads them early.
Related concepts
- function declarationused by · A function declaration is a source-language construct that specifies a function’s name and parameter interface, and may include its implementation.
- identifier registrationcontrasts with · The pre-execution process of recording declared identifiers and their initial bindings in a lexical environment.
- import statementuses · An import statement is a source-code declaration that makes names or definitions from another module, package, or namespace available in the current scope.
- bindingcontrasts with · Name binding is the association of an identifier with the program entity or value it denotes.
- variable declaration keywordcontrasts with · A variable declaration keyword is a programming-language keyword that introduces a variable binding.
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