--- /dev/null
+/**
+ * @fileoverview Rule to enforce that all class methods use 'this'.
+ * @author Patrick Williams
+ */
+
+"use strict";
+
+//------------------------------------------------------------------------------
+// Requirements
+//------------------------------------------------------------------------------
+
+const astUtils = require("./utils/ast-utils");
+
+//------------------------------------------------------------------------------
+// Rule Definition
+//------------------------------------------------------------------------------
+
+module.exports = {
+ meta: {
+ type: "suggestion",
+
+ docs: {
+ description: "enforce that class methods utilize `this`",
+ category: "Best Practices",
+ recommended: false,
+ url: "https://eslint.org/docs/rules/class-methods-use-this"
+ },
+
+ schema: [{
+ type: "object",
+ properties: {
+ exceptMethods: {
+ type: "array",
+ items: {
+ type: "string"
+ }
+ }
+ },
+ additionalProperties: false
+ }],
+
+ messages: {
+ missingThis: "Expected 'this' to be used by class {{name}}."
+ }
+ },
+ create(context) {
+ const config = Object.assign({}, context.options[0]);
+ const exceptMethods = new Set(config.exceptMethods || []);
+
+ const stack = [];
+
+ /**
+ * Initializes the current context to false and pushes it onto the stack.
+ * These booleans represent whether 'this' has been used in the context.
+ * @returns {void}
+ * @private
+ */
+ function enterFunction() {
+ stack.push(false);
+ }
+
+ /**
+ * Check if the node is an instance method
+ * @param {ASTNode} node node to check
+ * @returns {boolean} True if its an instance method
+ * @private
+ */
+ function isInstanceMethod(node) {
+ return !node.static && node.kind !== "constructor" && node.type === "MethodDefinition";
+ }
+
+ /**
+ * Check if the node is an instance method not excluded by config
+ * @param {ASTNode} node node to check
+ * @returns {boolean} True if it is an instance method, and not excluded by config
+ * @private
+ */
+ function isIncludedInstanceMethod(node) {
+ return isInstanceMethod(node) &&
+ (node.computed || !exceptMethods.has(node.key.name));
+ }
+
+ /**
+ * Checks if we are leaving a function that is a method, and reports if 'this' has not been used.
+ * Static methods and the constructor are exempt.
+ * Then pops the context off the stack.
+ * @param {ASTNode} node A function node that was entered.
+ * @returns {void}
+ * @private
+ */
+ function exitFunction(node) {
+ const methodUsesThis = stack.pop();
+
+ if (isIncludedInstanceMethod(node.parent) && !methodUsesThis) {
+ context.report({
+ node,
+ messageId: "missingThis",
+ data: {
+ name: astUtils.getFunctionNameWithKind(node)
+ }
+ });
+ }
+ }
+
+ /**
+ * Mark the current context as having used 'this'.
+ * @returns {void}
+ * @private
+ */
+ function markThisUsed() {
+ if (stack.length) {
+ stack[stack.length - 1] = true;
+ }
+ }
+
+ return {
+ FunctionDeclaration: enterFunction,
+ "FunctionDeclaration:exit": exitFunction,
+ FunctionExpression: enterFunction,
+ "FunctionExpression:exit": exitFunction,
+ ThisExpression: markThisUsed,
+ Super: markThisUsed
+ };
+ }
+};