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noDoubleEquals (since v1.0.0)

Diagnostic Category: lint/suspicious/noDoubleEquals

Sources:

Require the use of === and !==

It is generally bad practice to use == for comparison instead of ===. Double operators will trigger implicit type coercion and are thus not prefered. Using strict equality operators is almost always best practice.

For ergonomic reasons, this rule makes an exception for == null for comparing to both null and undefined.

Examples

Section titled Examples

Invalid

Section titled Invalid
foo == bar
code-block.js:1:5 lint/suspicious/noDoubleEquals  FIXABLE  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ✖ Use === instead of ==
  
  > 1 │ foo == bar
      │     ^^
    2 │ 
  
  ℹ == is only allowed when comparing against null
  
  > 1 │ foo == bar
      │     ^^
    2 │ 
  
  ℹ Using == may be unsafe if you are relying on type coercion
  
  ℹ Unsafe fix: Use ===
  
    1 │ foo·===·bar
      │       +

Valid

Section titled Valid
foo == null
foo != null
null == foo
null != foo
Section titled Related links