prefer-reflect

This rule was deprecated in ESLint v3.9.0 and will not be replaced. The original intent of this rule now seems misguided as we have come to understand that Reflect methods are not actually intended to replace the Object counterparts the rule suggests, but rather exist as low-level primitives to be used with proxies in order to replicate the default behavior of various previously existing functionality.

The ES6 Reflect API comes with a handful of methods which somewhat deprecate methods on old constructors:

• Reflect.apply effectively deprecates Function.prototype.apply and Function.prototype.call

• Reflect.deleteProperty effectively deprecates the delete keyword

• Reflect.getOwnPropertyDescriptor effectively deprecates Object.getOwnPropertyDescriptor

• Reflect.getPrototypeOf effectively deprecates Object.getPrototypeOf

• Reflect.setPrototypeOf effectively deprecates Object.setPrototypeOf

• Reflect.preventExtensions effectively deprecates Object.preventExtensions

The prefer-reflect rule will flag usage of any older method, suggesting to instead use the newer Reflect version.

Rule Details

Options

Exceptions

"prefer-reflect": [<enabled>, { "exceptions": [<...exceptions>] }]

The exceptions option allows you to pass an array of methods names you’d like to continue to use in the old style.

For example if you wish to use all Reflect methods, except for Function.prototype.apply then your config would look like prefer-reflect: [2, { "exceptions": ["apply"] }].

If you want to use Reflect methods, but keep using the delete keyword, then your config would look like prefer-reflect: [2, { "exceptions": ["delete"] }].

These can be combined as much as you like. To make all methods exceptions (thereby rendering this rule useless), use prefer-reflect: [2, { "exceptions": ["apply", "call", "defineProperty", "getOwnPropertyDescriptor", "getPrototypeOf", "setPrototypeOf", "isExtensible", "getOwnPropertyNames", "preventExtensions", "delete"] }]

Reflect.apply

Deprecates Function.prototype.apply() and Function.prototype.call()

Examples of incorrect code for this rule when used without exceptions:

/*eslint prefer-reflect: "error"*/

myFunction.apply(undefined, args);
myFunction.apply(null, args);
obj.myMethod.apply(obj, args);
obj.myMethod.apply(other, args);

myFunction.call(undefined, arg);
myFunction.call(null, arg);
obj.myMethod.call(obj, arg);
obj.myMethod.call(other, arg);

Examples of correct code for this rule when used without exceptions:

/*eslint prefer-reflect: "error"*/

Reflect.apply(myFunction, undefined, args);
Reflect.apply(myFunction, null, args);
Reflect.apply(obj.myMethod, obj, args);
Reflect.apply(obj.myMethod, other, args);
Reflect.apply(myFunction, undefined, [arg]);
Reflect.apply(myFunction, null, [arg]);
Reflect.apply(obj.myMethod, obj, [arg]);
Reflect.apply(obj.myMethod, other, [arg]);

Examples of correct code for this rule with the { "exceptions": ["apply"] } option:

/*eslint prefer-reflect: ["error", { "exceptions": ["apply"] }]*/

// in addition to Reflect.apply(...):
myFunction.apply(undefined, args);
myFunction.apply(null, args);
obj.myMethod.apply(obj, args);
obj.myMethod.apply(other, args);

Examples of correct code for this rule with the { "exceptions": ["call"] } option:

/*eslint prefer-reflect: ["error", { "exceptions": ["call"] }]*/

// in addition to Reflect.apply(...):
myFunction.call(undefined, arg);
myFunction.call(null, arg);
obj.myMethod.call(obj, arg);
obj.myMethod.call(other, arg);

Reflect.defineProperty

Deprecates Object.defineProperty()

Examples of incorrect code for this rule when used without exceptions:

/*eslint prefer-reflect: "error"*/

Object.defineProperty({}, 'foo', {value: 1})

Examples of correct code for this rule when used without exceptions:

/*eslint prefer-reflect: "error"*/

Reflect.defineProperty({}, 'foo', {value: 1})

Examples of correct code for this rule with the { "exceptions": ["defineProperty"] } option:

/*eslint prefer-reflect: ["error", { "exceptions": ["defineProperty"] }]*/

Object.defineProperty({}, 'foo', {value: 1})
Reflect.defineProperty({}, 'foo', {value: 1})

Reflect.getOwnPropertyDescriptor

Deprecates Object.getOwnPropertyDescriptor()

Examples of incorrect code for this rule when used without exceptions:

/*eslint prefer-reflect: "error"*/

Object.getOwnPropertyDescriptor({}, 'foo')

Examples of correct code for this rule when used without exceptions:

/*eslint prefer-reflect: "error"*/

Reflect.getOwnPropertyDescriptor({}, 'foo')

Examples of correct code for this rule with the { "exceptions": ["getOwnPropertyDescriptor"] } option:

/*eslint prefer-reflect: ["error", { "exceptions": ["getOwnPropertyDescriptor"] }]*/

Object.getOwnPropertyDescriptor({}, 'foo')
Reflect.getOwnPropertyDescriptor({}, 'foo')

Reflect.getPrototypeOf

Deprecates Object.getPrototypeOf()

Examples of incorrect code for this rule when used without exceptions:

/*eslint prefer-reflect: "error"*/

Object.getPrototypeOf({}, 'foo')

Examples of correct code for this rule when used without exceptions:

/*eslint prefer-reflect: "error"*/

Reflect.getPrototypeOf({}, 'foo')

Examples of correct code for this rule with the { "exceptions": ["getPrototypeOf"] } option:

/*eslint prefer-reflect: ["error", { "exceptions": ["getPrototypeOf"] }]*/

Object.getPrototypeOf({}, 'foo')
Reflect.getPrototypeOf({}, 'foo')

Reflect.setPrototypeOf

Deprecates Object.setPrototypeOf()

Examples of incorrect code for this rule when used without exceptions:

/*eslint prefer-reflect: "error"*/

Object.setPrototypeOf({}, Object.prototype)

Examples of correct code for this rule when used without exceptions:

/*eslint prefer-reflect: "error"*/

Reflect.setPrototypeOf({}, Object.prototype)

Examples of correct code for this rule with the { "exceptions": ["setPrototypeOf"] } option:

/*eslint prefer-reflect: ["error", { "exceptions": ["setPrototypeOf"] }]*/

Object.setPrototypeOf({}, Object.prototype)
Reflect.setPrototypeOf({}, Object.prototype)

Reflect.isExtensible

Deprecates Object.isExtensible

Examples of incorrect code for this rule when used without exceptions:

/*eslint prefer-reflect: "error"*/

Object.isExtensible({})

Examples of correct code for this rule when used without exceptions:

/*eslint prefer-reflect: "error"*/

Reflect.isExtensible({})

Examples of correct code for this rule with the { "exceptions": ["isExtensible"] } option:

/*eslint prefer-reflect: ["error", { "exceptions": ["isExtensible"] }]*/

Object.isExtensible({})
Reflect.isExtensible({})

Reflect.getOwnPropertyNames

Deprecates Object.getOwnPropertyNames()

Examples of incorrect code for this rule when used without exceptions:

/*eslint prefer-reflect: "error"*/

Object.getOwnPropertyNames({})

Examples of correct code for this rule when used without exceptions:

/*eslint prefer-reflect: "error"*/

Reflect.getOwnPropertyNames({})

Examples of correct code for this rule with the { "exceptions": ["getOwnPropertyNames"] } option:

/*eslint prefer-reflect: ["error", { "exceptions": ["getOwnPropertyNames"] }]*/

Object.getOwnPropertyNames({})
Reflect.getOwnPropertyNames({})

Reflect.preventExtensions

Deprecates Object.preventExtensions()

Examples of incorrect code for this rule when used without exceptions:

/*eslint prefer-reflect: "error"*/

Object.preventExtensions({})

Examples of correct code for this rule when used without exceptions:

/*eslint prefer-reflect: "error"*/

Reflect.preventExtensions({})

Examples of correct code for this rule with the { "exceptions": ["preventExtensions"] } option:

/*eslint prefer-reflect: ["error", { "exceptions": ["preventExtensions"] }]*/

Object.preventExtensions({})
Reflect.preventExtensions({})

Reflect.deleteProperty

Deprecates the delete keyword

Examples of incorrect code for this rule when used without exceptions:

/*eslint prefer-reflect: "error"*/

delete foo.bar; // deleting object property

Examples of correct code for this rule when used without exceptions:

/*eslint prefer-reflect: "error"*/

delete bar; // deleting variable
Reflect.deleteProperty(foo, 'bar');

Note: For a rule preventing deletion of variables, see no-delete-var instead

Examples of correct code for this rule with the { "exceptions": ["delete"] } option:

/*eslint prefer-reflect: ["error", { "exceptions": ["delete"] }]*/

delete bar
delete foo.bar
Reflect.deleteProperty(foo, 'bar');

When Not To Use It

This rule should not be used in ES3/5 environments.

In ES2015 (ES6) or later, if you don’t want to be notified about places where Reflect could be used, you can safely disable this rule.

Related Rules

• no-useless-call

• prefer-spread

• no-delete-var

Version

This rule was introduced in ESLint 1.0.0-rc-2.

Resources

• Rule source

• Documentation source

 © JS Foundation and other contributors

Licensed under the MIT License.

https://eslint.org/docs/rules/prefer-reflect