[Deff]

var str='return el == " this "'
function TstThis(str){
var a=str.replace(/^.*?((?:["']\s*)?this(?:["']\s*)?)/i,'$1').replace(/\s/ig,'');
 return!(a.indexOf("'this'")!=-1||a.indexOf('"this"')!=-1)
}

var str='return el == " this "'
alert(TstThis(str))
var str='return el == this'
alert(TstThis(str))
var str='return el == "bla-bla-bla this \"foo" && this'
alert(TstThis(str))