code: function getNumber() {
    const type = NodeType.NumberType;
    const token = tokens[pos];
    const line = token.ln;
    const column = token.col;
    const l = tokens[pos].number_l;
    let content = '';
  
    for (let j = 0; j < l; j++) {
      content += tokens[pos + j].value;
    }
  
    pos += l;
  
    return newNode(type, content, line, column);
  }
docs: Get node with number
  @return {Array} `['number', x]` where `x` is a number converted
  to string.