eqeqeq

== and != convert their operands before comparing them, so "" == 0 and [] == false are both true. === and !== compare without converting.

Configure

Off by default. To turn it on:

[lint.rules]
"eqeqeq" = "error" # or "warn"

Every option, set to its default:

[lint.rules]
"eqeqeq" = [
  "error",
  "always", # "always", "smart" or "allow-null"
  {
    null = "always", # "always", "never" or "ignore"
  },
]

Examples

Reported:

if (count == 0) {
  reset();
}

Not reported:

if (count === 0) {
  reset();
}

Options

[lint.rules]
eqeqeq = ["error", "smart"]

Option	What it does
"always" (default)	Report every == and !=.
"smart"	Allow == when comparing with null, comparing two literals, or comparing the result of typeof.

With "always", a second option decides what happens with null: { "null": "always" } (default) reports x == null, "ignore" allows it, and "never" reports x === null instead.

With "smart", this is allowed, because == null is a common way to test for both null and undefined:

if (value == null) {
  value = fallback;
}

And this is still reported:

if (value == other) {
  merge(value, other);
}