eslint-plugin-lit/lib/rules/no-this-assign-in-render.js

lit-html support for ESLint

/**
 * @fileoverview Disallows assignments to members of `this` in render methods
 * @author James Garbutt <https://github.com/43081j>
 */
import { isLitClass } from '../util.js';
//------------------------------------------------------------------------------
// Rule Definition
//------------------------------------------------------------------------------
export const rule = {
    meta: {
        docs: {
            description: 'Disallows assignments to members of `this` in render methods',
            recommended: false,
            url: 'https://github.com/43081j/eslint-plugin-lit/blob/master/docs/rules/no-this-assign-in-render.md'
        },
        schema: [],
        messages: {
            noThis: 'Members of `this` should not be assigned to in the render ' +
                'method. It is likely you should do this elsewhere instead ' +
                '(e.g. in `updated`)'
        }
    },
    create(context) {
        let inRender = false;
        let inComponent = false;
        /**
         * Class entered
         *
         * @param {ESTree.Class} node Node entered
         * @return {void}
         */
        function classEnter(node) {
            if (!isLitClass(node, context)) {
                return;
            }
            inComponent = true;
        }
        /**
         * Class exited
         *
         * @return {void}
         */
        function classExit() {
            inComponent = false;
        }
        /**
         * Method entered
         *
         * @param {ESTree.MethodDefinition} node Node entered
         * @return {void}
         */
        function methodEnter(node) {
            if (!inComponent ||
                node.kind !== 'method' ||
                node.static === true ||
                node.key.type !== 'Identifier' ||
                node.key.name !== 'render') {
                return;
            }
            inRender = true;
        }
        /**
         * Method exited
         *
         * @return {void}
         */
        function methodExit() {
            inRender = false;
        }
        /**
         * Left side of an assignment expr found
         *
         * @param {Rule.Node} node Node entered
         * @return {void}
         */
        function assignmentFound(node) {
            if (!inRender || !node.parent) {
                return;
            }
            context.report({
                node: node.parent,
                messageId: 'noThis'
            });
        }
        return {
            ClassExpression: (node) => classEnter(node),
            ClassDeclaration: (node) => classEnter(node),
            'ClassExpression:exit': classExit,
            'ClassDeclaration:exit': classExit,
            MethodDefinition: (node) => methodEnter(node),
            'MethodDefinition:exit': methodExit,
            'AssignmentExpression > .left:has(ThisExpression)': (node) => assignmentFound(node)
        };
    }
};