Function To Check Mutliple Text Box Inputs?

I have this form which has 4 fields that must not be empty on submit, I been trying to make an array that checks them.

<form action="login.php" method="post" onsubmit="return(checkAll(this))">
<label>Username<br /><input id="input[]" type="text" name="username" /></label><br />
<label>Email<br /><input id="input[]" type="text" name="email" /></label><br />
<label>Password<br /><input id="input[]" type="password" name="pswd1" /></label><br />
<label>Password Again<br /><input id="input[] "type="password" name="pswd2" /></label><br />

[Code]...