JavaScript swap問題，求大神指點，重謝！

var?firstEl?=?document.getElementById(firstId);

var?secondEl?=?document.getElementById(secondId);

var?temp?=?firstEl.innerHTML;

firstEl.innerHTML?=?secondEl.innerHTML;

secondEl.innerHTML?=?temp;

}

function?clearit(){

var?printBtn?=?document.createElement('input');

printBtn.id?=?'printBtn';

printBtn.type?=?'button';

printBtn.value?=?'print';

printBtn.onclick?=?printit;

document.body.appendChild(printBtn);

}

function?printit(){

alert('print?called');

}