I have a problem with a validate function, I made it in one function only and I want to add validation of email such as @ and numbers 1-9. How do I add it?

html:

<form onsubmit=return validate(); name=formValidation>

    <label>First Name:</label>

    <input type=text name=firstName /><br /><br />

    <label>Last Name:</label>

    <input type=text name=lastName /><br /><br />

    <label>E_mail:</label>

    <input type=text name=Email /><br /><br />

    <label>Confirm E_mail:</label>

    <input type=text name=confirmEmail /><br /><br />

    <label>Address:</label>

    <input type=text name=Address /><br /><br />

    <label>Telephone nr:</label>

    <input type=text name=telephoneNr /><br /><br />

    <br />

    <p>submit your form: </p><input type=submit value=Submit />

</form>

js:

function validate(){

    if(document.formValidation.firstName.value ==  ||

    document.formValidation.lastName.value ==  ||

    document.formValidation.Email.value ==  ||

    document.formValidation.confirmEmail.value ==  ||

    document.formValidation.Address.value ==  ||

    document.formValidation.telephoneNr.value == )

    {

        alert(Please fill all the boxes before submitting!);

        return false;

    } else {

        alert('Your form has been submitted!');

    }



}