noUndeclaredVariables

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Diagnostic Category: lint/correctness/noUndeclaredVariables

JavaScript (and super languages)

Since: v1.0.0 Sources:

Same as: no-undef

Description

Prevents the usage of variables that haven’t been declared inside the document.

If you need to allow-list some global bindings, you can use the javascript.globals configuration.

Options (Since v2.0.0)

The rule provides a checkTypes option that make the rule checks undeclared types. The option defaults to true.

{
    "options": {
        "checkTypes": true
    }
}

Examples

Invalid

foobar;

code-block.js:1:1 lint/correctness/noUndeclaredVariables ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ⚠ The foobar variable is undeclared.
  
  > 1 │ foobar;
      │ ^^^^^^
    2 │ 
  
  ℹ By default, Biome recognizes browser and Node.js globals.
    You can ignore more globals using the javascript.globals configuration.

// throw diagnostic for JavaScript files
PromiseLike;

code-block.js:2:1 lint/correctness/noUndeclaredVariables ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ⚠ The PromiseLike variable is undeclared.
  
    1 │ // throw diagnostic for JavaScript files
  > 2 │ PromiseLike;
      │ ^^^^^^^^^^^
    3 │ 
  
  ℹ By default, Biome recognizes browser and Node.js globals.
    You can ignore more globals using the javascript.globals configuration.

Valid

type B<T> = PromiseLike<T>

How to configure

{
  "linter": {
    "rules": {
      "correctness": {
        "noUndeclaredVariables": "error"
      }
    }
  }
}