Variable declaration keyword
A variable declaration keyword is a programming-language keyword that introduces a variable binding.
Get Programming with JavaScript Next: New features of ECMAScript 2015, 2016, and beyond
A JavaScript keyword that declares a block-scoped local variable whose binding cannot be accessed outside the block where it is declared.
- How it is used
- Keeps changing JavaScript variables local to blocks, especially loops, instead of letting function-scoped declarations escape their intended use.
- How deep it goes
- Explains block scope, loop behavior, hoisting, and temporal-dead-zone errors through examples, stopping at observable behavior rather than engine internals.
- Examples
- Contrasts delayed loop callbacks, hides data in a free-standing block, and challenges readers to remove IIFEs from a range function.
- What you can do after
- Practice/perform block-scoped declarations in loops and replace IIFEs used only to contain local variables.
Secrets of the JavaScript Ninja, Second Edition
A JavaScript keyword used to declare a variable binding, such as var, let, or const.
- How it is used
- Distinguishes JavaScript variable declarations by mutability and relationship to the lexical environment.
- 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.
Read how Secrets of the JavaScript Ninja, Second Edition explains variable declaration keyword →
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.
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