noFlatMapIdentity (since v1.7.0)

Diagnostic Category: lint/nursery/noFlatMapIdentity

Sources:

Same as: flat_map_identity

Disallow to use unnecessary callback on flatMap.

To achieve the same result (flattening an array) more concisely and efficiently, you should use flat instead.

Examples

Invalid

array.flatMap((arr) => arr);

nursery/noFlatMapIdentity.js:1:1 lint/nursery/noFlatMapIdentity  FIXABLE  ━━━━━━━━━━━━━━━━━━━━━━━━━━

  ✖ Avoid unnecessary callback in flatMap call.
  
  > 1 │ array.flatMap((arr) => arr);
      │ ^^^^^^^^^^^^^^^^^^^^^^^^^^^
    2 │ 
  
  ℹ You can just use flat to flatten the array.
  
  ℹ Safe fix: Replace unnecessary flatMap call to flat instead.
  
    1   │ - array.flatMap((arr)·=>·arr);
      1 │ + array.flat();
    2 2 │

array.flatMap((arr) => {return arr});

nursery/noFlatMapIdentity.js:1:1 lint/nursery/noFlatMapIdentity  FIXABLE  ━━━━━━━━━━━━━━━━━━━━━━━━━━

  ✖ Avoid unnecessary callback in flatMap call.
  
  > 1 │ array.flatMap((arr) => {return arr});
      │ ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    2 │ 
  
  ℹ You can just use flat to flatten the array.
  
  ℹ Safe fix: Replace unnecessary flatMap call to flat instead.
  
    1   │ - array.flatMap((arr)·=>·{return·arr});
      1 │ + array.flat();
    2 2 │

Valid

array.flatMap((arr) => arr * 2);