Disallow this
keywords outside of classes or class-like objects. (no-invalid-this)
Under the strict mode, this
keywords outside of classes or class-like objects might be undefined
and raise a TypeError
.
Rule Details
This rule aims to flag usage of this
keywords outside of classes or class-like objects.
Basically this rule checks whether or not a function which are containing this
keywords is a constructor or a method.
This rule judges from 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 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. (excepts static methods)
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()
) ifthisArg
is given. - The function has
@this
tag in its JSDoc comment.
Otherwise are considered problems.
This rule applies only in strict mode. With "parserOptions": { "sourceType": "module" }
in the ESLint configuration, your code is in strict mode even without a "use strict"
directive.
Examples of incorrect code for this rule in strict mode:
/*eslint no-invalid-this: "error"*/
/*eslint-env es6*/
"use strict";
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 in 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 in strict mode:
/*eslint no-invalid-this: "error"*/
/*eslint-env es6*/
"use strict";
function Foo() {
// OK, this is in a legacy style constructor.
this.a = 0;
baz(() => this);
}
class Foo {
constructor() {
// OK, this is in a constructor.
this.a = 0;
baz(() => this);
}
}
var obj = {
foo: function foo() {
// OK, this is in a method (this function is on object literal).
this.a = 0;
}
};
var obj = {
foo() {
// OK, this is in a method (this function is on object literal).
this.a = 0;
}
};
var obj = {
get foo() {
// OK, this is in a method (this function is on object literal).
return this.a;
}
};
var obj = Object.create(null, {
foo: {value: function foo() {
// OK, this is in a method (this function is on object literal).
this.a = 0;
}}
});
Object.defineProperty(obj, "foo", {
value: function foo() {
// OK, this is in a method (this function is on object literal).
this.a = 0;
}
});
Object.defineProperties(obj, {
foo: {value: function foo() {
// OK, this is in a method (this function is on object literal).
this.a = 0;
}}
});
function Foo() {
this.foo = function foo() {
// OK, this is in a method (this function assigns to a property).
this.a = 0;
baz(() => this);
};
}
obj.foo = function foo() {
// OK, this is in a method (this function assigns to a property).
this.a = 0;
};
Foo.prototype.foo = function foo() {
// OK, this is in a method (this function assigns to a property).
this.a = 0;
};
class Foo {
foo() {
// OK, this is in a method.
this.a = 0;
baz(() => this);
}
static foo() {
// OK, this is in a method (static methods also have valid this).
this.a = 0;
baz(() => this);
}
}
var foo = (function foo() {
// OK, the `bind` method of this function is called directly.
this.a = 0;
}).bind(obj);
foo.forEach(function() {
// OK, `thisArg` of `.forEach()` is given.
this.a = 0;
baz(() => this);
}, thisArg);
/** @this Foo */
function foo() {
// OK, this function has a `@this` tag in its JSDoc comment.
this.a = 0;
}
When Not To Use It
If you don't want to be notified about usage of this
keyword outside of classes or class-like objects, you can safely disable this rule.
Version
This rule was introduced in ESLint 1.0.0-rc-2.