Possible Errors

Best Practices

Strict Mode

Variables

init-declarations

Require or disallow initialization in variable declarations

no-delete-var

Disallow deleting variables

no-label-var

Disallow labels that share a name with a variable

no-restricted-globals

Disallow specified global variables

no-shadow

Disallow variable declarations from shadowing variables declared in the outer scope

no-shadow-restricted-names

Disallow identifiers from shadowing restricted names

no-undef

Disallow the use of undeclared variables unless mentioned in /*global */ comments

no-undef-init

Disallow initializing variables to undefined

no-undefined

Disallow the use of undefined as an identifier

no-unused-vars

Disallow unused variables

no-use-before-define

Disallow the use of variables before they are defined

Node.js and CommonJS

Stylistic Issues

ECMAScript 6

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no-undefined

- Disallow the use of undefined as an identifier

This rule aims to eliminate the use of undefined, and as such, generates a warning whenever it is used.

What ESLint should do when it catches the rule break

Show a warning

Rule examples

You can check them out here.

no-undef-init no-unused-vars