astorphysics: May 2026

JavaScript `==` Type Coercion Table

Expression	Result	Why?
`0 == false`	`true`	`false` is coerced to `0`
`0 == ""`	`true`	`""` is coerced to `0`
`"" == false`	`true`	Both become `0`
`"0" == false`	`true`	`"0"` → `0`, `false` → `0`
`null == undefined`	`true`	Special rule in JS spec
`null == 0`	`false`	No coercion between `null` and numbers
`undefined == 0`	`false`	No coercion between `undefined` and numbers
`"5" == 5`	`true`	`"5"` → `5`
`true == 1`	`true`	`true` → `1`
`true == 2`	`false`	`true` → `1`, `1 != 2`
`[] == ""`	`true`	`[]` → `""`
`[] == 0`	`true`	`[]` → `""` → `0`
`[""] == 0`	`true`	`[""]` → `""` → `0`
`[1] == 1`	`true`	`[1]` → `"1"` → `1`
`[] == false`	`true`	`[]` → `""` → `0`, `false` → `0`
`[null] == 0`	`true`	`[null]` → `""` → `0`
`["0"] == false`	`true`	`"0"` → `0`, `false` → `0`

== can be confusing because it tries to convert values to a common type.
null and undefined are only loosely equal to each other, not to anything else.
Arrays and objects are converted to primitives before comparison.
Always prefer === unless you really want these coercion rules.