If click the submit button or a
-element then automatically the input text is clicked.
function send()
{
var txt = document.getElementById("textbox");
txt.click();
}
<input type="text" id="textbox" name="textbox" style="width:90%;">
<a id="send" style="display:none;" onclick="send()" href="">Send</a>
If you want to get the value of "textbox" with the following instruction:
var txt = document.getElementById("textbox");
Then you need to correct it like this:
var txt = document.getElementById("textbox").value;