var length = typeof '문자열' === 'string' && '문자열'.length; var isString1 = typeof (new String('문자열')) === 'string' && (new String('문자열')).length > 0; var isString2 = typeof (new String('문자열')) === 'object' && (new String('문자열')).length > 0; var isString3 = typeof new String('문자열').valueOf() === 'string' && (new String('문자열')).length > 0; alert(length); alert(isString1); alert(isString2); alert(isString3);