code: function (pos) {
              if (pos === undefined) {
                  pos = this.position;
              }
              var lines = this.source.substring(0, pos).split(/\r?\n/),
                  row = lines.length,
                  col = lines.pop().length + 1,
                  allLines = this.source.split(/\r?\n/),
                  source = [];
              for (var i = -2; i < 2; i++) {
                  if (allLines[row + i]) {
                      source.push({
                          row: row + i + 1,
                          code: allLines[row + i]
                      })
                  }
              }
              return {
                  row: row,
                  col: col,
                  source: source
              }
          }
docs: 获取指定位置字符所在的行号、列号、该行的上一行和下两行。Get the line number for the position.
  @returns {{row: Number, col: *, source: Array}}