code: function spaces(node) {
              const tokens = getTokens(node);
              const countSpace = countSpaces(tokens);
  
              if (rule.before) {
  
                  // should be space(s) before arrow
                  if (countSpace.before === 0) {
                      context.report({
                          node: tokens.before,
                          messageId: "expectedBefore",
                          fix(fixer) {
                              return fixer.insertTextBefore(tokens.arrow, " ");
                          }
                      });
                  }
              } else {
  
                  // should be no space before arrow
                  if (countSpace.before > 0) {
                      context.report({
                          node: tokens.before,
                          messageId: "unexpectedBefore",
                          fix(fixer) {
                              return fixer.removeRange([tokens.before.range[1], tokens.arrow.range[0]]);
                          }
                      });
                  }
              }
  
              if (rule.after) {
  
                  // should be space(s) after arrow
                  if (countSpace.after === 0) {
                      context.report({
                          node: tokens.after,
                          messageId: "expectedAfter",
                          fix(fixer) {
                              return fixer.insertTextAfter(tokens.arrow, " ");
                          }
                      });
                  }
              } else {
  
                  // should be no space after arrow
                  if (countSpace.after > 0) {
                      context.report({
                          node: tokens.after,
                          messageId: "unexpectedAfter",
                          fix(fixer) {
                              return fixer.removeRange([tokens.arrow.range[1], tokens.after.range[0]]);
                          }
                      });
                  }
              }
          }
docs: Determines whether space(s) before after arrow(`=>`) is satisfy rule.
  if before/after value is `true`, there should be space(s).
  if before/after value is `false`, there should be no space.
  @param {ASTNode} node The arrow function node.
  @returns {void}