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1、
document.getElementById('foo')
==>
$('foo')
2、
var woot = document.getElementById('bar').valuevar
woot = $('bar').value
==>
var woot = $F('bar')
3、
$('footer').style.height = '100px';
$('footer').style.background = '#ffc';   
==>
$('footer').setStyle({
    height: '100px',
    background: '#ffc'
})
4、
$('coolestWidgetEver').innerHTML = 'some nifty content'
==>
$('coolestWidgetEver').update('some nifty content')