Using JS new RegExp is so much slower (about 500 times) than Regexp

A small talk about performance and where the results I'm getting are coming from.

CONTEXT

I'm trying to use a RegExp to get all the matches possible and get a 100 char before and after the match. I use two types of RegExp handling in this case

The 'direct' RegExp looking like that :

myString.match(/[\s\S]{0,100}SomethingImTryingToFind[\s\S]{0,100}/ig);

And the new RegExp looking like that :

myString.match(new RegExp('[\\s\\S]{0,100}SomethingImTryingToFind[\\s\\S]{0,100}', 'ig'))

What's the problem here ?

Now let's say we get some data set on which I wanna use my previous search, I then created two methods that are exactly the same, besides the line written above and look like that.

function getNewRegexpHits(elem) {
            var count = 0;
            elem.foundKeys = [];
            Object.keys(elem).forEach(function(key){
                if(typeof elem[key] === 'string') {
                    elem[key + '_founds'] = (elem[key] || '').match(new RegExp('[\\s\\S]{0,100}e[\\s\\S]{0,100}', 'ig')) || [];
                    elem[key + '_count'] = elem[key + '_founds'].length;
                    count += elem[key + '_count'];
                    if (elem[key + '_count'] > 0) {
                        elem.foundKeys.push(key);
                    }
                }
            });
            elem.totalFound = count;
            return count;
        }

Now I'm just running a basic performance comparison between those two by doing something like that :

 results = someFetchingReturningALargeDataSet();
 var t0 = performance.now();
 results.hits.forEach(function(elem){
     getHits(elem);
 });
 var t1 = performance.now();
 console.log("Call to getHits took " + (t1 - t0) + " milliseconds.");
 var t2 = performance.now();
 results.hits.forEach(function(elem){
     getNewRegexpHits(elem);
 });
 var t3 = performance.now();
 console.log("Call to getNewRegexpHits took " + (t3 - t2) + " milliseconds.");

Now both methods work fine and I get the expected results both time but look at the performance issue now .. This is the console output :

Any ideas why that might be ? I actually need to use the new Regexp because I need to use a variable parameter instead of "SomethingImTryingToFind"