There are several ways in which one might imagine optimzing a regular expression that is often used.
The first is to simply create it each time using new RegExp(), as follows:

function insideLoop() {
  var it = iterations;
  for(var i=0; i<it; i++) {
    var myRegExpIn = new RegExp("there");
    myRegExpIn.test("hello there man");
  }
}

The second way would be to skip the "new RegExp()" stuff, since it's just a static string that we're matching against, and, instead, use this:

function insideLoop2() {
  var it = iterations;
  for(var i=0; i<it; i++) {
    /there/.test("hello there man");
  }
}

What would appear to be the obvious way of optimizing this if it's done often enough, is to create a global variable for this RegExp and just always reference that, like so:

var myRegExpOut = /there/;
function outsideLoop() {
  var it = iterations;
  for(var i=0; i<it; i++) {
    myRegExpOut.test("hello there man");
  }
}

Click the 'Measure' button below to see how they stack up with run 10,000 times: