no-useless-computed-key

Disallow unnecessary computed property keys in objects and classes

It’s unnecessary to use computed properties with literals such as:

var foo = {["a"]: "b"};
1

The code can be rewritten as:

var foo = {"a": "b"};
1

Rule Details

This rule disallows unnecessary usage of computed property keys.

Examples of incorrect code for this rule:

/*eslint no-useless-computed-key: "error"*/

var a = { ['0']: 0 };
var a = { ['0+1,234']: 0 };
var a = { [0]: 0 };
var a = { ['x']: 0 };
var a = { ['x']() {} };

class Foo {
    ["foo"] = "bar";

    [0]() {}
    ['a']() {}
    get ['b']() {}
    set ['c'](value) {}

    static ["foo"] = "bar";

    static ['a']() {}
}
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20

Examples of correct code for this rule:

/*eslint no-useless-computed-key: "error"*/

var c = { 'a': 0 };
var c = { 0: 0 };
var a = { x() {} };
var c = { a: 0 };
var c = { '0+1,234': 0 };

class Foo {
    "foo" = "bar";

    0() {}
    'a'() {}
    get 'b'() {}
    set 'c'(value) {}

    static "foo" = "bar";

    static 'a'() {}
}
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20

Examples of additional correct code for this rule:

/*eslint no-useless-computed-key: "error"*/

var c = {
    "__proto__": foo, // defines object's prototype

    ["__proto__"]: bar // defines a property named "__proto__"
};

class Foo {
    ["constructor"]; // instance field named "constructor"

    "constructor"() {} // the constructor of this class

    ["constructor"]() {} // method named "constructor"

    static ["constructor"]; // static field named "constructor"

    static ["prototype"]; // runtime error, it would be a parsing error without `[]`
}
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19

Options

This rule has an object option:

• enforceForClassMembers set to false disables this rule for class members (Default true).

enforceForClassMembers

By default, this rule also checks class declarations and class expressions, as the default value for enforceForClassMembers is true.

When enforceForClassMembers is set to false, the rule will allow unnecessary computed keys inside of class fields, class methods, class getters, and class setters.

Examples of incorrect code for this rule with the { "enforceForClassMembers": false } option:

/*eslint no-useless-computed-key: ["error", { "enforceForClassMembers": false }]*/

const obj = {
    ["foo"]: "bar",
    [42]: "baz",

    ['a']() {},
    get ['b']() {},
    set ['c'](value) {}
};
1
2
3
4
5
6
7
8
9
10

Examples of correct code for this rule with the { "enforceForClassMembers": false } option:

/*eslint no-useless-computed-key: ["error", { "enforceForClassMembers": false }]*/

class SomeClass {
    ["foo"] = "bar";
    [42] = "baz";

    ['a']() {}
    get ['b']() {}
    set ['c'](value) {}

    static ["foo"] = "bar";
    static ['baz']() {}
}
1
2
3
4
5
6
7
8
9
10
11
12
13

When Not To Use It

If you don’t want to be notified about unnecessary computed property keys, you can safely disable this rule.

Version

This rule was introduced in ESLint v2.9.0.

Resources

• Rule source
• Tests source