Right now we use codemirror's JavaScript mode on the website but there's a JSX mode now so we should start using that instead.

this.collapse(lines);
        this.children = [new LeafChunk(lines)];
        this.children[0].parent = this;
      }
    },
    collapse: function(lines) {
      for (var i = 0, e = this.children.length; i < e; ++i) this.children[i].collapse(lines);
    },
    insertInner: function(at, lines, height) {
      this.size += lines.length;
      this.height += height;
      for (var i = 0, e = this.children.length; i < e; ++i) {
        var child = this.children[i], sz = child.chunkSize();
        if (at <= sz) {
          child.insertInner(at, lines, height);
          if (child.lines && child.lines.length > 50) {
            while (child.lines.length > 50) {
              var spilled = child.lines.splice(child.lines.length - 25, 25);
              var newleaf = new LeafChunk(spilled);
              child.height -= newleaf.height;
              this.children.splice(i + 1, 0, newleaf);
              newleaf.parent = this;
            }
            this.maybeSpill();
          }
          break;
        }
        at -= sz;
      }
    },