getRange(node) {
    if (node == null) {
      return null;
    }
    if (this._ranges.has(node)) {
      return this._ranges.get(node);
    }
    const {nodeToRange} = this._adapterOptions;
    let range = nodeToRange(node);
    if (node && typeof node === 'object') {
      this._ranges.set(node, range);
    }
    return range;
  }
The start and end indicies of the node in the source text. The return value
is an array of form `[start, end]`. This is used for highlighting source
text and focusing nodes in the tree.