#no-invalid-this

#Configuration

import { defineConfig, ts } from '@rslint/core';

export default defineConfig([
  ts.configs.recommended,
  {
    rules: {
      '@typescript-eslint/no-invalid-this': 'error',
    },
  },
]);

Disallow this keywords outside of classes or class-like objects.

#Rule Details

Under strict mode, this keywords outside of classes or class-like objects might be undefined and raise a TypeError.

This rule judges from the following conditions whether or not the function is a constructor:

• The name of the function starts with uppercase.
• The function is assigned to a variable which starts with an uppercase letter.
• The function is a constructor of ES2015 Classes.

This rule judges from the following conditions whether or not the function is a method:

• The function is on an object literal.
• The function is assigned to a property.
• The function is a method / getter / setter of ES2015 Classes.

And this rule allows this keywords in functions below:

• The call / apply / bind method of the function is called directly.
• The function is a callback of array methods (such as .forEach()) if thisArg is given.
• The function has an @this tag in its JSDoc comment.
• The function declares an explicit this parameter (function foo(this: SomeType)).

Otherwise, this rule warns on this keywords. It also reports this at the top level.

Examples of incorrect code for this rule:

this.a = 0;
baz(() => this);

(function () {
  this.a = 0;
  baz(() => this);
})();

function foo() {
  this.a = 0;
  baz(() => this);
}

var foo = function () {
  this.a = 0;
  baz(() => this);
};

foo(function () {
  this.a = 0;
  baz(() => this);
});

obj.foo = () => {
  // `this` of arrow functions is the outer scope's.
  this.a = 0;
};

var obj = {
  aaa: function () {
    return function foo() {
      // There is a method `aaa`, but `foo` is not a method.
      this.a = 0;
      baz(() => this);
    };
  },
};

foo.forEach(function () {
  this.a = 0;
  baz(() => this);
});

Examples of correct code for this rule:

function Foo() {
  // OK, legacy-style constructor.
  this.a = 0;
  baz(() => this);
}

class Foo {
  constructor() {
    this.a = 0;
    baz(() => this);
  }
}

var obj = {
  foo() {
    this.a = 0;
  },
};

var obj = {
  get foo() {
    return this.a;
  },
};

Object.defineProperty(obj, 'foo', {
  value: function foo() {
    this.a = 0;
  },
});

obj.foo = function foo() {
  this.a = 0;
};

class Foo {
  foo() {
    this.a = 0;
    baz(() => this);
  }

  static foo() {
    this.a = 0;
    baz(() => this);
  }
}

var foo = function foo() {
  this.a = 0;
}.bind(obj);

foo.forEach(function () {
  this.a = 0;
  baz(() => this);
}, thisArg);

/** @this Foo */
function foo() {
  this.a = 0;
}

function foo(this: SomeType) {
  this.a = 0;
}

#Options

#capIsConstructor

Type: boolean — Default: true

When true, the rule treats a function whose name starts with an uppercase letter (or which is assigned to such a variable) as an ES5 constructor — this inside is allowed. Set this option to false to treat capitalized-name functions as regular functions.

Examples of incorrect code with { "capIsConstructor": false }:

{ "@typescript-eslint/no-invalid-this": ["error", { "capIsConstructor": false }] }

function Foo() {
  this.a = 0;
}

var Bar = function () {
  this.a = 0;
};

Baz = function () {
  this.a = 0;
};

Examples of correct code with { "capIsConstructor": false }:

{ "@typescript-eslint/no-invalid-this": ["error", { "capIsConstructor": false }] }

obj.Foo = function () {
  // OK, assigned to a property.
  this.a = 0;
};

class Foo {
  constructor() {
    this.a = 0;
  }
}

#When Not To Use It

If you do not want to be notified about usage of the this keyword outside of classes or class-like objects, you can safely disable this rule.

#Original Documentation

• typescript-eslint no-invalid-this
• ESLint no-invalid-this