eslint/rules/variables

Variables: Declarations, scope, shadowing, assignments and destructuring. Rules of ESLint, typescript-eslint and SonarJS (the Sonar way profile of SonarQube) on this subject, every rule listed; the TypeScript rules apply to TypeScript files only.

55 rules, 30 on. Source: lint/eslint/rules/variables.mjs.

Rule	Setting	Files	What it checks	Why
no-const-assign	error	JS + TS	Disallow reassigning const, using, and await using variables	—
no-dupe-args	error	JS + TS	Disallow duplicate arguments in function definitions	—
no-inner-declarations	error	JS + TS	Disallow variable or function declarations in nested blocks	—
no-unassigned-vars	error	JS + TS	Disallow let or var variables that are read but never assigned	—
no-undef	error	JS + TS	Disallow the use of undeclared variables unless mentioned in /*global */ comments	—
no-unused-vars	error	JS + TS	Disallow unused variables	Replaced by the TS version.
no-use-before-define	error	JS + TS	Disallow the use of variables before they are defined	Replaced by the TS version.
block-scoped-var	warn	JS + TS	Enforce the use of variables within the scope they are defined	—
init-declarations	off	JS + TS	Require or disallow initialization in variable declarations	Off: non-standard, forbids let x: T; assigned later.
no-delete-var	warn	JS + TS	Disallow deleting variables	—
no-global-assign	error	JS + TS	Disallow assignments to native objects or read-only global variables	—
no-implicit-globals	error	JS + TS	Disallow declarations in the global scope	—
no-multi-assign	info, {"ignoreNonDeclaration":true}	JS + TS	Disallow use of chained assignment expressions	a = b = 0 is allowed, const a = (b = 0) is not.
no-redeclare	error	JS + TS	Disallow variable redeclaration	Replaced by the TS version (a type and a value may not share a name either).
no-restricted-globals	off	JS + TS	Disallow specified global variables	—
no-shadow	warn	JS + TS	Disallow variable declarations from shadowing variables declared in the outer scope	Replaced by the TS version.
no-undef-init	off	JS + TS	Disallow initializing variables to undefined	—
no-useless-rename	error	JS + TS	Disallow renaming import, export, and destructured assignments to the same name	—
no-var	error	JS + TS	Require let or const instead of var	—
no-with	error	JS + TS	Disallow with statements	—
one-var	error, "never"	JS + TS	Enforce variables to be declared either together or separately in functions	One declaration per statement (cleaner diffs).
prefer-const	error, {"destructuring":"all"}	JS + TS	Require const declarations for variables that are never reassigned after declared	Destructuring is reported only when every variable could be const.
prefer-destructuring	error	JS + TS	Require destructuring from arrays and/or objects	Replaced by the TS version.
vars-on-top	off	JS + TS	Require var declarations be placed at the top of their containing scope	Off: var is forbidden (no-var).
sonarjs/destructuring-assignment-syntax	off	JS + TS	Destructuring syntax should be used for assignments	Off: not in the Sonar way profile of SonarQube.
sonarjs/block-scoped-var	off	JS + TS	Variables should be used in the blocks where they are declared	Off: duplicate of block-scoped-var.
sonarjs/no-delete-var	off	JS + TS	"delete" should be used only with object properties	Off: duplicate of no-delete-var.
sonarjs/no-globals-shadowing	off	JS + TS	Special identifiers should not be bound or assigned	Off: duplicate of no-shadow-restricted-names.
sonarjs/no-implicit-global	off	JS + TS	Variables should be declared explicitly	Off: duplicate of no-undef (and a TypeScript compiler error).
sonarjs/no-unused-vars	off	JS + TS	Unused local variables and functions should be removed	Off: duplicate of @typescript-eslint/no-unused-vars (which honours the _ prefix).
sonarjs/declarations-in-global-scope	off	JS + TS	Variables and functions should not be declared in the global scope	Off: not in the Sonar way profile of SonarQube.
sonarjs/no-mixed-completion-style	off	JS + TS	Test and hook callbacks should use a single completion style	Off: not in the Sonar way profile of SonarQube.
sonarjs/no-nested-assignment	warn	JS + TS	Assignments should not be made from within sub-expressions	—
sonarjs/no-redundant-assignments	warn	JS + TS	Assignments should not be redundant	—
sonarjs/no-variable-usage-before-declaration	off	JS + TS	Variables declared with "var" should be declared before they are used	Off: not in the Sonar way profile of SonarQube.
no-const-assign	off	TS	Disallow reassigning const, using, and await using variables	—
no-dupe-args	off	TS	Disallow duplicate arguments in function definitions	—
no-undef	off	TS	Disallow the use of undeclared variables unless mentioned in /*global */ comments	—
no-with	off	TS	Disallow with statements	—
no-delete-var	off	TS	Disallow deleting variables	—
no-implicit-globals	off	TS	Disallow declarations in the global scope	—
@typescript-eslint/init-declarations	off	TS	Require or disallow initialization in variable declarations	Off: see core rule. If enabled, write ['error', 'always'] (ESLint 10 passes no default mode).
@typescript-eslint/no-dynamic-delete	warn	TS	Disallow using the delete operator on computed key expressions	—
no-redeclare	off	TS	Disallow variable redeclaration	Replaced by the TS version (a type and a value may not share a name either).
@typescript-eslint/no-redeclare	error, {"ignoreDeclarationMerge":false}	TS	Disallow variable redeclaration	—
no-shadow	off	TS	Disallow variable declarations from shadowing variables declared in the outer scope	Replaced by the TS version.
@typescript-eslint/no-shadow	warn	TS	Disallow variable declarations from shadowing variables declared in the outer scope	—
no-unused-vars	off	TS	Disallow unused variables	Replaced by the TS version.
@typescript-eslint/no-unused-vars	error, {"argsIgnorePattern":"^_","varsIgnorePattern":"^_","caugh…	TS	Disallow unused variables	_ prefix = intentionally unused.
no-use-before-define	off	TS	Disallow the use of variables before they are defined	Replaced by the TS version.
@typescript-eslint/no-use-before-define	error, {"functions":false}	TS	Disallow the use of variables before they are defined	Hoisted function declarations may be used before their definition.
@typescript-eslint/no-useless-default-assignment	info	TS	Disallow default values that will never be used	—
@typescript-eslint/prefer-as-const	error	TS	Enforce the use of as const over literal type	—
prefer-destructuring	off	TS	Require destructuring from arrays and/or objects	Replaced by the TS version.
@typescript-eslint/prefer-destructuring	error	TS	Require destructuring from arrays and/or objects	—