When JavaScript guesses what you meant

Python raises a TypeError if you add a string to a number. JavaScript instead performs type coercionJavaScript's habit of silently converting between types when an operator gets operands it did not expect.: it silently converts one operand and carries on. Coming from Python, this is the single most surprising thing about the language, because the program does not stop. It produces a plausible-looking wrong answer. What makes it worse is that the rule is not uniform across operators. + is overloaded: it means both numeric addition and string concatenation, so if either side is a string, JavaScript concatenates. Every other arithmetic operator has no string meaning at all, so it converts both sides to numbers instead.