JavaScript’s Weirdest Comparison

Source: Dev.to

Why [] == false is true

[] == false   // true

The == operator performs type coercion:

1. false is converted to 0.
2. [] is first converted to an empty string "".
3. The empty string "" is then converted to 0.

Thus the comparison becomes:

0 == 0   // true

Why [] == ![] is true

[] == ![]   // true

Evaluation steps:

1. ![] – an empty array is truthy, so applying ! yields false.
2. The expression now is [] == false, which we already know evaluates to true (see above).

Takeaway

The == operator can produce surprising results because of implicit type conversion.
Most developers prefer the strict equality operator ===, which does not perform coercion and therefore avoids these pitfalls.

[] === false   // false
[] === ![]     // false

Understanding how coercion works removes the “weirdness” from JavaScript comparisons. Happy coding! ✨