no-invalid-this.js

/**
 * @fileoverview A rule to disallow `this` keywords in contexts where the value of `this` is `undefined`.
 * @author Toru Nagashima
 */

"use strict";

//------------------------------------------------------------------------------
// Requirements
//------------------------------------------------------------------------------

const astUtils = require("./utils/ast-utils");

//------------------------------------------------------------------------------
// Helpers
//------------------------------------------------------------------------------

/**
 * Determines if the given code path is a code path with lexical `this` binding.
 * That is, if `this` within the code path refers to `this` of surrounding code path.
 * @param {CodePath} codePath Code path.
 * @param {ASTNode} node Node that started the code path.
 * @returns {boolean} `true` if it is a code path with lexical `this` binding.
 */
function isCodePathWithLexicalThis(codePath, node) {
    return codePath.origin === "function" && node.type === "ArrowFunctionExpression";
}

//------------------------------------------------------------------------------
// Rule Definition
//------------------------------------------------------------------------------

/** @type {import('../shared/types').Rule} */
module.exports = {
    meta: {
        type: "suggestion",

        docs: {
            description: "Disallow use of `this` in contexts where the value of `this` is `undefined`",
            recommended: false,
            url: "https://eslint.org/docs/latest/rules/no-invalid-this"
        },

        schema: [
            {
                type: "object",
                properties: {
                    capIsConstructor: {
                        type: "boolean",
                        default: true
                    }
                },
                additionalProperties: false
            }
        ],

        messages: {
            unexpectedThis: "Unexpected 'this'."
        }
    },

    create(context) {
        const options = context.options[0] || {};
        const capIsConstructor = options.capIsConstructor !== false;
        const stack = [],
            sourceCode = context.sourceCode;

        /**
         * Gets the current checking context.
         *
         * The return value has a flag that whether or not `this` keyword is valid.
         * The flag is initialized when got at the first time.
         * @returns {{valid: boolean}}
         *   an object which has a flag that whether or not `this` keyword is valid.
         */
        stack.getCurrent = function() {
            const current = this[this.length - 1];

            if (!current.init) {
                current.init = true;
                current.valid = !astUtils.isDefaultThisBinding(
                    current.node,
                    sourceCode,
                    { capIsConstructor }
                );
            }
            return current;
        };

        return {

            onCodePathStart(codePath, node) {
                if (isCodePathWithLexicalThis(codePath, node)) {
                    return;
                }

                if (codePath.origin === "program") {
                    const scope = sourceCode.getScope(node);
                    const features = context.parserOptions.ecmaFeatures || {};

                    // `this` at the top level of scripts always refers to the global object
                    stack.push({
                        init: true,
                        node,
                        valid: !(
                            node.sourceType === "module" ||
                            (features.globalReturn && scope.childScopes[0].isStrict)
                        )
                    });

                    return;
                }

                /*
                 * `init: false` means that `valid` isn't determined yet.
                 * Most functions don't use `this`, and the calculation for `valid`
                 * is relatively costly, so we'll calculate it lazily when the first
                 * `this` within the function is traversed. A special case are non-strict
                 * functions, because `this` refers to the global object and therefore is
                 * always valid, so we can set `init: true` right away.
                 */
                stack.push({
                    init: !sourceCode.getScope(node).isStrict,
                    node,
                    valid: true
                });
            },

            onCodePathEnd(codePath, node) {
                if (isCodePathWithLexicalThis(codePath, node)) {
                    return;
                }

                stack.pop();
            },

            // Reports if `this` of the current context is invalid.
            ThisExpression(node) {
                const current = stack.getCurrent();

                if (current && !current.valid) {
                    context.report({
                        node,
                        messageId: "unexpectedThis"
                    });
                }
            }
        };
    }
};