including php variable in javascript function

how can i include a php variable (eg. $textstring) into javascript function

Here's the code:

<script>
function insertText() {
var textstring = "test string";
document.getElementById ("{$editorid}_iframe").contentWindow.document.body.innerHTML += textstring;
document.getElementById('vB_Editor_001_textarea').value += textstring;
}
</script>

Code (markup):

<a href="javascript:;" onClick="insertText()">test</a>

HTML:

I just want to insert $textstring instead of var textstring ($textstring which is identified in php script)

Thanks in advance,

 

var textstring = "<?=$textstring ?>";

 

thanks for your help

 

When $textstring is more than 1 line it doesnt work, is there a way around this?

using \n doesnt work for iframes and it would make the line too long

EDIT: Found solution