Type coercion means that when the operands of an operator are different types, one of them will be converted to an “equivalent” value of the other operand’s type. For instance, if you do:
boolean == integer
the boolean operand will be converted to an integer: false
becomes 0
, true
becomes 1. Then the two values are compared.
However, if you use the non-converting comparison operator ===
, no such conversion occurs. When the operands are of different types, this operator returns false
, and only compares the values when they’re of the same type.
You can find a good explanation of JavaScript’s coercion rules in You Don’t Know JS and more reference-oriented documentation in MDN.