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/**
* @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
};
}
};
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