Simple Javascript email verification

Here is a simple email verification script in Javascript.  Just pass in the email address and it will return true or false depending on if the email is valid.  It will also do an alert popup if it is invalid.

function echeck(str) {

var at="@"

var dot="."

var lat=str.indexOf(at)

var lstr=str.length

var ldot=str.indexOf(dot)

if (str.indexOf(at)==-1){

  alert("Invalid email address of attendee.")

  return false

}

if (str.indexOf(at)==-1 || str.indexOf(at)==0 || str.indexOf(at)==lstr){

  alert("Invalid email address of attendee.")

  return false

}

if (str.indexOf(dot)==-1 || str.indexOf(dot)==0 || str.indexOf(dot)==lstr){

   alert("Invalid email address of attendee.")

   return false

}

if (str.indexOf(at,(lat+1))!=-1){

   alert("Invalid email address of attendee.")

   return false

}

if (str.substring(lat-1,lat)==dot || str.substring(lat+1,lat+2)==dot){

   alert("Invalid email address of attendee.")

   return false

}

if (str.indexOf(dot,(lat+2))==-1){

   alert("Invalid email address of attendee.")

   return false

}

if (str.indexOf(" ")!=-1){

   alert("Invalid email address of attendee.")

   return false

}

  return true

}

Got this thanks to: Javascript Email Address Validation