--- /dev/null
+/**
+ * @fileoverview enforce "for" loop update clause moving the counter in the right direction.(for-direction)
+ * @author Aladdin-ADD<hh_2013@foxmail.com>
+ */
+
+"use strict";
+
+//------------------------------------------------------------------------------
+// Rule Definition
+//------------------------------------------------------------------------------
+
+module.exports = {
+ meta: {
+ type: "problem",
+
+ docs: {
+ description: "enforce \"for\" loop update clause moving the counter in the right direction.",
+ category: "Possible Errors",
+ recommended: true,
+ url: "https://eslint.org/docs/rules/for-direction"
+ },
+
+ fixable: null,
+ schema: [],
+
+ messages: {
+ incorrectDirection: "The update clause in this loop moves the variable in the wrong direction."
+ }
+ },
+
+ create(context) {
+
+ /**
+ * report an error.
+ * @param {ASTNode} node the node to report.
+ * @returns {void}
+ */
+ function report(node) {
+ context.report({
+ node,
+ messageId: "incorrectDirection"
+ });
+ }
+
+ /**
+ * check the right side of the assignment
+ * @param {ASTNode} update UpdateExpression to check
+ * @param {int} dir expected direction that could either be turned around or invalidated
+ * @returns {int} return dir, the negated dir or zero if it's not clear for identifiers
+ */
+ function getRightDirection(update, dir) {
+ if (update.right.type === "UnaryExpression") {
+ if (update.right.operator === "-") {
+ return -dir;
+ }
+ } else if (update.right.type === "Identifier") {
+ return 0;
+ }
+ return dir;
+ }
+
+ /**
+ * check UpdateExpression add/sub the counter
+ * @param {ASTNode} update UpdateExpression to check
+ * @param {string} counter variable name to check
+ * @returns {int} if add return 1, if sub return -1, if nochange, return 0
+ */
+ function getUpdateDirection(update, counter) {
+ if (update.argument.type === "Identifier" && update.argument.name === counter) {
+ if (update.operator === "++") {
+ return 1;
+ }
+ if (update.operator === "--") {
+ return -1;
+ }
+ }
+ return 0;
+ }
+
+ /**
+ * check AssignmentExpression add/sub the counter
+ * @param {ASTNode} update AssignmentExpression to check
+ * @param {string} counter variable name to check
+ * @returns {int} if add return 1, if sub return -1, if nochange, return 0
+ */
+ function getAssignmentDirection(update, counter) {
+ if (update.left.name === counter) {
+ if (update.operator === "+=") {
+ return getRightDirection(update, 1);
+ }
+ if (update.operator === "-=") {
+ return getRightDirection(update, -1);
+ }
+ }
+ return 0;
+ }
+ return {
+ ForStatement(node) {
+
+ if (node.test && node.test.type === "BinaryExpression" && node.test.left.type === "Identifier" && node.update) {
+ const counter = node.test.left.name;
+ const operator = node.test.operator;
+ const update = node.update;
+
+ let wrongDirection;
+
+ if (operator === "<" || operator === "<=") {
+ wrongDirection = -1;
+ } else if (operator === ">" || operator === ">=") {
+ wrongDirection = 1;
+ } else {
+ return;
+ }
+
+ if (update.type === "UpdateExpression") {
+ if (getUpdateDirection(update, counter) === wrongDirection) {
+ report(node);
+ }
+ } else if (update.type === "AssignmentExpression" && getAssignmentDirection(update, counter) === wrongDirection) {
+ report(node);
+ }
+ }
+ }
+ };
+ }
+};