Javascript - Array.repeat limitations?

You can build a simple function to do this:

var triples = function(xs) {
  return xs.map(function(x) {
    return [x,x,x].join(' ')
  })
}

You can abstract it a bit more, as a transformation to use with map, and allow any number of repetitions:

var repeat = function(n) {
  return function(x) {
    return Array.apply(0, {length:n})
      .map(function(){return x})
      .join(' ')
  }
}

['foo','bar','lol'].map(repeat(3))
//^ ['foo foo foo', 'bar bar bar', 'lol lol lol']

Here's an obnoxiously simple way of repeating all elements 3 times:

["red", "green", "blue"].map(  [].join.bind(['',' ',' ',''])   );
// == ["red red red", "green green green", "blue blue blue"]

this method also doesn't need "".repeat(), which is not universally supported yet.

another bonus: if a number, null, or other non-string sneaks in the array it won't break.

if you want it re-usable, that's easy enough:

 var repeater = [].join.bind(['',' ',' ','']) ;

 ["red", "green", "blue"].map( repeater );
 // == ["red red red", "green green green", "blue blue blue"]

 [1,2,3,4,5].map( repeater );
 // == ["1 1 1", "2 2 2", "3 3 3", "4 4 4", "5 5 5"]

There is no reason to use map and the loop. I guess you wanted either

var triples = myArray.map(function(str){
  return str.repeat(3);
});
console.log(triples);

or

var triples = [];
for (var x = 0; x < myArray.length; x++) {
  triples[x] = myArray[x].repeat(3);
}
console.log(triples);

However, as @digitalfresh mentioned in the comments, String::repeat doesn't insert the spaces, so you rather want to use (" "+…).repeat(3).slice(1) or use the functions presented by @dandavis or @elclanrs. Or, since you seem to use an Ecmascript 6 method anyway, you could do Array.from({length:3}, ()=>…).join(" ").