x|0 is a standard idiom, as explained in the ECMAScript Spec: The production A : A @ B, where @ is one of the bitwise operators in the productions above, i

x|0 is a standard idiom, as explained in the ECMAScript Spec: The production A : A @ B, where @ is one of the bitwise operators in the productions above, is evaluated as follows: - Let lref be the result of evaluating A. - Let lval be GetValue(lref). - Let rref be the result of evaluating B. - Let rval be GetValue(rref). - Let lnum be ToInt32(lval).* <-- Convert to 32 bit Integer - Let rnum be ToInt32(rval).* - Return the result of applying the bitwise operator @ to lnum and rnum. The result is a signed 32 bit integer. x|0 is therefore the result of ToInt32(x), which is effectively a coercion to integer. Directed link to the section in the annotated spec: http://es5.github.com/#x11.10 http://es5.github.com/#x11.10 (or http://ecma-international.org/ecma-262/5.1/#sec-11.10 http://ecma-international.org/ecma-262/5.1/#sec-11.10 -- as evilpie pointed out in a reply) For the original spec, read Pages 82-83 of http://www.ecma-international.org/publications/files/ECMA-ST/Ecma-262.pdf http://www.ecma-international.org/publications/files/ECMA-ST...