⏎ Lint Rules

noBannedTypes (since v10.0.0)

Disallow certain types.

Some built-in types have aliases, while some types are considered dangerous or harmful. It’s often a good idea to ban certain types to help with consistency and safety.

This rule bans specific types and can suggest alternatives. Note that it doesn’t ban the corresponding runtime objects from being used.

Source: https://typescript-eslint.io/rules/ban-types

Examples

Invalid

let foo: String = "bar";

nursery/noBannedTypes.js:1:10 lint/nursery/noBannedTypes  FIXABLE  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ⚠ Don't use 'String' as a type.
  
  > 1 │ let foo: String = "bar";
      │          ^^^^^^
    2 │ 
  
  ℹ Use lowercase primitives for consistency.
  
  ℹ Safe fix: Use 'string' instead
  
    1   │ - let·foo:·String·=·"bar";
      1 │ + let·foo:·string·=·"bar";
    2 2 │   
  

let bool = true as Boolean;

nursery/noBannedTypes.js:1:20 lint/nursery/noBannedTypes  FIXABLE  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ⚠ Don't use 'Boolean' as a type.
  
  > 1 │ let bool = true as Boolean;
      │                    ^^^^^^^
    2 │ 
  
  ℹ Use lowercase primitives for consistency.
  
  ℹ Safe fix: Use 'boolean' instead
  
    1   │ - let·bool·=·true·as·Boolean;
      1 │ + let·bool·=·true·as·boolean;
    2 2 │   
  

let invalidTuple: [string, Boolean] = ["foo", false];

nursery/noBannedTypes.js:1:28 lint/nursery/noBannedTypes  FIXABLE  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ⚠ Don't use 'Boolean' as a type.
  
  > 1 │ let invalidTuple: [string, Boolean] = ["foo", false];
      │                            ^^^^^^^
    2 │ 
  
  ℹ Use lowercase primitives for consistency.
  
  ℹ Safe fix: Use 'boolean' instead
  
    1   │ - let·invalidTuple:·[string,·Boolean]·=·["foo",·false];
      1 │ + let·invalidTuple:·[string,·boolean]·=·["foo",·false];
    2 2 │   
  

Valid

let foo: string = "bar";

let tuple: [boolean, string] = [false, "foo"];