Edit in JSFiddle

// 변수선언
var trueStr = "true";
var falseStr = "false";
var trueUppercaseStr = "TRUE";
var falseUppercaseStr = "FALSE";

// 변환메소드 메소드 내용만 보면 됨.
function convertBoolean( str ) {
	return JSON.parse( str.toLowerCase() );
}


write( trueStr );
write( falseStr );
write( trueUppercaseStr );
write( falseUppercaseStr );

document.write( "<br/>" )

write( convertBoolean( trueStr ) );
write( convertBoolean( falseStr ) );
write( convertBoolean( trueUppercaseStr ) );
write( convertBoolean( falseUppercaseStr ) );

function write( message ) {
	document.write( "<li>" + message + ", " + ( typeof message ) + "</li>")
}