More elegant array multiplication than multiple concat statements Background

Trevor wishes to duplicate an array, transforming it by multiplying its elements four times.

Existing Solution

//
var atest =   ['a','b','c'];
var btest =   [];
btest     =   atest.concat(atest).concat(atest).concat(atest);
//
console.log(btest.length);  // btest.length == 12
console.log(btest);         // ["a", "b", "c", "a", "b", "c", "a", "b", "c", "a", "b", "c"] 


Goal

Trevor does not like this because it is ugly. Can you help Trevor find his happy place again? It's bugging Trevor.
Here's one that uses call and manually concat a

var a = ['a','b','c'], b = Array.prototype.concat.call(a,a,a,a);


If you wanted an easy way to variably add a, just change i:

for(var a=["a","b","c"],b=[],i=4;i--;) b.push.apply(b,a);