8000 [FEAT] [no-this-alias] Add rule (#232) · kaicataldo/typescript-eslint@ebee203 · GitHub
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[FEAT] [no-this-alias] Add rule (typescript-eslint#232)
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‎packages/eslint-plugin-typescript/README.md

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| [`typescript/no-non-null-assertion`](./docs/rules/no-non-null-assertion.md) | Disallows non-null assertions using the `!` postfix operator (`no-non-null-assertion` from TSLint) | | |
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| [`typescript/no-object-literal-type-assertion`](./docs/rules/no-object-literal-type-assertion.md) | Forbids an object literal to appear in a type assertion expression (`no-object-literal-type-assertion` from TSLint) | | |
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| [`typescript/no-parameter-properties`](./docs/rules/no-parameter-properties.md) | Disallow the use of parameter properties in class constructors. (`no-parameter-properties` from TSLint) | | |
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| [`typescript/no-this-alias`](./docs/rules/no-this-alias.md) | Disallow aliasing `this` (`no-this-assignment` from TSLint) | | |
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| [`typescript/no-triple-slash-reference`](./docs/rules/no-triple-slash-reference.md) | Disallow `/// <reference path="" />` comments (`no-reference` from TSLint) | | |
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| [`typescript/no-type-alias`](./docs/rules/no-type-alias.md) | Disallow the use of type aliases (`interface-over-type-literal` from TSLint) | | |
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| [`typescript/no-unused-vars`](./docs/rules/no-unused-vars.md) | Prevent TypeScript-specific constructs from being erroneously flagged as unused | :heavy_check_mark: | |

‎packages/eslint-plugin-typescript/docs/rules/no-this-alias.md

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# Disallow aliasing `this` (no-this-alias)
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This rule prohibts assigning variables to `this`.
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## Rule Details
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Rationale from TSLint:
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> Assigning a variable to `this` instead of properly using arrow lambdas may be a symptom of pre-ES6 practices
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> or not managing scope well.
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>
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> Instead of storing a reference to `this` and using it inside a `function () {`:
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>
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> ```js
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> const self = this;
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>
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> setTimeout(function () {
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> self.doWork();
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> });
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> ```
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>
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> Use `() =>` arrow lambdas, as they preserve `this` scope for you:
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>
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> ```js
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> setTimeout(() => {
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> this.doWork();
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> });
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> ```
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Examples of **incorrect** code for this rule:
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(see the rationale above)
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Examples of **correct** code for this rule:
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(see the rationale above)
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### Options
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You can pass an object option:
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```json5
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{
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"typescript/no-this-alias": ["error", {
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"allowDestructuring": true, // Allow `const { props, state } = this`; false by default
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"allowedNames": ["self"], // Allow `const self = this`; `[]` by default
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}],
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}
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```
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## When Not To Use It
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If you need to assign `this` to variables, you shouldn’t use this rule.
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## Related to
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- TSLint: [`no-this-assignment`](https://palantir.github.io/tslint/rules/no-this-assignment/)

‎packages/eslint-plugin-typescript/lib/rules/no-this-alias.js

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/**
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* @fileoverview Disallow aliasing `this`
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* @author Jed Fox
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*/
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"use strict";
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const util = require("../util");
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//------------------------------------------------------------------------------
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// Rule Definition
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//------------------------------------------------------------------------------
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module.exports = {
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meta: {
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docs: {
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description: "Disallow aliasing `this`",
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extraDescription: [util.tslintRule("no-this-assignment")],
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category: "Best Practices",
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recommended: false,
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url: util.metaDocsUrl("no-this-alias"),
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},
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fixable: null,
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schema: [
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{
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type: "object",
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additionalProperties: false,
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properties: {
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allowDestructuring: {
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type: "boolean",
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},
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allowedNames: {
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type: "array",
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items: {
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type: "string",
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},
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},
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},
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},
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],
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messages: {
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thisAssignment: "Unexpected aliasing of 'this' to local variable.",
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thisDestructure:
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"Unexpected aliasing of members of 'this' to local variables.",
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},
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},
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create(context) {
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const { allowDestructuring = false, allowedNames = [] } =
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context.options[0] || {};
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return {
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VariableDeclarator(node) {
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const { id, init } = node;
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if (init.type !== "ThisExpression") return;
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if (allowDestructuring && node.id.type !== "Identifier") return;
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if (!allowedNames.includes(id.name)) {
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context.report({
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node: id,
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messageId:
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id.type === "Identifier"
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? "thisAssignment"
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: "thisDestructure",
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});
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}
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},
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};
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},
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};

‎packages/eslint-plugin-typescript/tests/lib/rules/no-this-alias.js

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/**
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* @fileoverview Disallow aliasing `this`
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* Some tests taken from TSLint: https://github.com/palantir/tslint/tree/c7fc99b5/test/rules/no-this-assignment
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* @author Jed Fox
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*/
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"use strict";
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//------------------------------------------------------------------------------
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// Requirements
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//------------------------------------------------------------------------------
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const rule = require("../../../lib/rules/no-this-alias"),
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RuleTester = require("eslint").RuleTester;
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const idError = { messageId: "thisAssignment", type: "Identifier" };
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const destructureError = {
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messageId: "thisDestructure",
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type: "ObjectPattern",
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};
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const arrayDestructureError = {
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messageId: "thisDestructure",
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type: "ArrayPattern",
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};
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//------------------------------------------------------------------------------
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// Tests
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//------------------------------------------------------------------------------
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const ruleTester = new RuleTester({
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parser: "typescript-eslint-parser",
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});
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ruleTester.run("no-this-alias", rule, {
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valid: [
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"const self = foo(this);",
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{
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code: `
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const { props, state } = this;
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const { length } = this;
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const { length, toString } = this;
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const [foo] = this;
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const [foo, bar] = this;
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`.trim(),
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options: [
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{
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allowDestructuring: true,
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},
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],
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},
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{
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code: "const self = this;",
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options: [
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{
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allowedNames: ["self"],
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},
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],
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},
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],
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invalid: [
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{
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code: "const self = this;",
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options: [
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{
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allowDestructuring: true,
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},
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],
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errors: [idError],
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},
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{
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code: "const self = this;",
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errors: [idError],
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},
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{
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code: "const { props, state } = this;",
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errors: [destructureError],
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},
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{
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code: `
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var unscoped = this;
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function testFunction() {
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let inFunction = this;
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}
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const testLambda = () => {
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const inLambda = this;
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};
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`.trim(),
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errors: [idError, idError, idError],
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},
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{
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code: `
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class TestClass {
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constructor() {
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const inConstructor = this;
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const asThis: this = this;
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const asString = "this";
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const asArray = [this];
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const asArrayString = ["this"];
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}
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public act(scope: this = this) {
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const inMemberFunction = this;
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const { act } = this;
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const { act, constructor } = this;
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const [foo] = this;
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const [foo, bar] = this;
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}
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}
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`.trim(),
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errors: [
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idError,
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idError,
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idError,
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destructureError,
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destructureError,
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arrayDestructureError,
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arrayDestructureError,
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],
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},
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],
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});

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