<textarea id="wiyetxt"></textarea>
<input type="button" onclick="test();" value="Send">
<input type="reset" value="Clear">

var substr = "test substr";
function test() {
  var textareaVal = $("#wiyetxt").val();
  if (substr.indexOf(textareaVal) !== -1) {
    alert("Found");
  }
  else {
    alert("Nope");
  }
}