Javascript Array of Arrays Manipulation

I am a beginner and getting confused about this. I am trying to insert brackets '['and ']' into the 'text' array below in order to make an array of arrays and am unable to figure it out. Can anyone please advise? Thank you all.

var text = [
1, 
2, 3, 
4, 5, 6, 
]

should become

var text = [
[1], 
[2, 3], 
[4, 5, 6], 
]

I found this from a previous Stack thread but am not sure how to implement it thought I think it is one possible method for attacking this:

String.prototype.insert = function (index, string) {
  if (index > 0)
    return this.substring(0, index) + string + this.substring(index, this.length);
  else
    return string + this;
};

// var something = "How you?";
// something = something.insert(3, " are");