Discord GitHub GitHub Twitter

Lint Rules

noSelfCompare (since v12.0.0)

Disallow comparisons where both sides are exactly the same.

Comparing a variable against itself is usually an error, either a typo or refactoring error. It is confusing to the reader and may potentially introduce a runtime error.

The only time you would compare a variable against itself is when you are testing for NaN. However, it is far more appropriate to use typeof x === 'number' && isNaN(x) or the Number.isNaN ES2015 function for that use case rather than leaving the reader of the code to determine the intent of self comparison.

Source: no-self-compare.

Examples

Invalid

if (x === x) {}
nursery/noSelfCompare.js:1:5 lint/nursery/noSelfCompare ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ✖ Comparing to itself is potentially pointless.
  
  > 1 │ if (x === x) {}
      │     ^^^^^^^
    2 │ 
  

if (a.b.c() !== a.b .c()) {}
nursery/noSelfCompare.js:1:5 lint/nursery/noSelfCompare ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ✖ Comparing to itself is potentially pointless.
  
  > 1 │ if (a.b.c() !== a.b .c()) {}
      │     ^^^^^^^^^^^^^^^^^^^^
    2 │