[Solved] Java Script, Need help finding my error [closed]

Should be

if ( score>==90 ) 
 {
    document.write ( "Your grade is an A." )
 }
else if ( score >==80 )
{
    document.write ( "Your grade is a B." )
} 
else if ( score >==70 )
{
    document.write ( "Your grade is a C.")
}
else if ( score >==60 ) 
 {
    document.write ( "Your grade is a D.")
 }
else if ( score >==0 )
{
    document.write ( "Your grade is a F")
 }