This test checks that BOM is treated as whitespace as required by ES5, but other Cf characters are not, despite what ECMA-262v3 says, see . On success, you will see a series of "PASS" messages, followed by "TEST COMPLETE". PASS escape(testString) is '%uFEFF%u200F%u200E%AD%u2062%u200D%u200C%u200B' PASS escape(testString2) is '%uFEFF%u200F%u200E%AD%u2062%u200D%u200C%u200B' PASS 1 is 1 PASS eval('""').length is 1 PASS eval('""').charCodeAt(0) is 0xFEFF PASS ++1 /* BOM between the +'s */ is 1 PASS var ZWJ_I‍nside; threw exception SyntaxError: Parse error. PASS successfullyParsed is true TEST COMPLETE