JavaScript uses var, let, and const to declare variables. They differ in mutability and in their relationship to the lexical environment. section 5.5
The three declaration keywords are:
- var section 5.5
- let section 5.5
- const section 5.5
Variable declaration keyword
A JavaScript keyword used to declare a variable binding, such as var, let, or const.
How Secrets of the JavaScript Ninja, Second Edition covers it
- How deep it goes
- Compares three declaration keywords by two properties: mutability and relationship to the lexical environment.
- Examples
- Names var, let, and const as the three declaration keywords.
- What you can do after
- Understand the comparison of var, let, and const by mutability and lexical-environment relationship.
- How it connects
- Connects variable declarations to lexical environments, closures, and scope.
Also explained in
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Get Programming with JavaScript Next: New features of ECMAScript 2015, 2016, and beyondA JavaScript keyword that declares a block-scoped local variable whose binding cannot be accessed outside the block where it is declared.
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Related concepts
- bindingcontrasts with · Name binding is the association of an identifier with the program entity or value it denotes.
- scopeuses · Scope is the region of a program in which names are visible and can be resolved according to the language’s lookup rules.
- const qualifiercontrasts with · A language feature that marks a value, binding, or access path as constant, restricting reassignment or modification according to the language’s rules.
- hoistingcontrasts with · Hoisting is JavaScript behavior in which certain declarations are registered within their scope before execution reaches their textual position.
- immediately invoked function expressionaddresses · 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.
- lexical environmentconfigures · A structure that associates identifiers with bindings and provides the context for resolving names at a point in program execution.
This explainer was generated by Manning's knowledge graph from the text of Secrets of the JavaScript Ninja, Second Edition. The section links point to the parts of the book it draws on.