about the number Literals lexical

Question

alert(010),the result is 8. why? i read the ecmascript 7.8.3 Numeric Literals. According to the Numeric Literals Lexical, 010 is a invalid numeric literals.

Answer 1

It's only so when strict mode is turned on :

(function(){
"use strict";
010;
})();
SyntaxError: Octal literals are not allowed in strict mode.

Otherwise it would break backwards compatibility.