Edit in JSFiddle

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

function convertBoolean( str ) {
	return str.toLowerCase() === "true";
}

function convertBooleanJson( str ) {
	return str.toLowerCase() === "true";
}

var startDate = new Date();
for( var i=0; i<1000000; i++ ) {
  convertBoolean( trueStr );
  convertBoolean( falseStr );
  convertBoolean( trueUppercaseStr );
  convertBoolean( falseUppercaseStr );
}
var endDate = new Date();

write( "단순비교 : " + ( endDate.getTime() - startDate.getTime() ) + "ms" );

write( "<br/>" );

startDate = new Date();
for( var i=0; i<1000000; i++ ) {
  convertBooleanJson( trueStr );
  convertBooleanJson( falseStr );
  convertBooleanJson( trueUppercaseStr );
  convertBooleanJson( falseUppercaseStr );
}
endDate = new Date();

write( "JSON : " +  ( endDate.getTime() - startDate.getTime() ) + "ms" );



function write( message ) {
	document.write( message );
}