@stylistic/js/

quote-props

Object literal property names can be defined in two ways: using literals or using strings. For example, these two objects are equivalent:

var object1 = {
    property: true
};

var object2 = {
    "property": true
};

In many cases, it doesn't matter if you choose to use an identifier instead of a string or vice-versa. Even so, you might decide to enforce a consistent style in your code.

There are, however, some occasions when you must use quotes:

1. If you are using an ECMAScript 3 JavaScript engine (such as IE8) and you want to use a keyword (such as if) as a property name. This restriction was removed in ECMAScript 5.
2. You want to use a non-identifier character in your property name, such as having a property with a space like "one two".

Another example where quotes do matter is when using numeric literals as property keys:

var object = {
    1e2: 1,
    100: 2
};

This may look alright at first sight, but this code in fact throws a syntax error in ECMAScript 5 strict mode. This happens because 1e2 and 100 are coerced into strings before getting used as the property name. Both String(1e2) and String(100) happen to be equal to "100", which causes the "Duplicate data property in object literal not allowed in strict mode" error. Issues like that can be tricky to debug, so some prefer to require quotes around all property names.

Rule Details

This rule requires quotes around object literal property names.

Options

This rule has two options, a string option and an object option.

String option:

• "always" (default) requires quotes around all object literal property names
• "as-needed" disallows quotes around object literal property names that are not strictly required
• "consistent" enforces a consistent quote style; in a given object, either all of the properties should be quoted, or none of the properties should be quoted
• "consistent-as-needed" requires quotes around all object literal property names if any name strictly requires quotes, otherwise disallows quotes around object property names

Object option:

• "keywords": true requires quotes around language keywords used as object property names (only applies when using as-needed or consistent-as-needed)
• "unnecessary": true (default) disallows quotes around object literal property names that are not strictly required (only applies when using as-needed)
• "unnecessary": false allows quotes around object literal property names that are not strictly required (only applies when using as-needed)
• "numbers": true requires quotes around numbers used as object property names (only applies when using as-needed)

always

Examples of incorrect code for this rule with the default "always" option:

/*eslint @stylistic/js/quote-props: ["error", "always"]*/

var object = {
        
foo: "bar"
,
        
baz: 42
};

incorrect

Examples of correct code for this rule with the default "always" option:

/*eslint @stylistic/js/quote-props: ["error", "always"]*/
/*eslint-env es6*/

var object1 = {
    "foo": "bar",
    "baz": 42,
    "qux-lorem": true
};

var object2 = {
    'foo': 'bar',
    'baz': 42,
    'qux-lorem': true
};

var object3 = {
    foo() {
        return;
    }
};

correct

as-needed

Examples of incorrect code for this rule with the "as-needed" option:

/*eslint @stylistic/js/quote-props: ["error", "as-needed"]*/

var object = {
        
"a": 0
,
        
"0": 0
,
        
"true": 0
,
        
"null": 0
};

incorrect

Examples of correct code for this rule with the "as-needed" option:

/*eslint @stylistic/js/quote-props: ["error", "as-needed"]*/
/*eslint-env es6*/

var object1 = {
    "a-b": 0,
    "0x0": 0,
    "1e2": 0
};

var object2 = {
    foo: 'bar',
    baz: 42,
    true: 0,
    0: 0,
    'qux-lorem': true
};

var object3 = {
    foo() {
        return;
    }
};

correct

consistent

Examples of incorrect code for this rule with the "consistent" option:

/*eslint @stylistic/js/quote-props: ["error", "consistent"]*/

var object1 = {
        
foo: "bar"
,
    "baz": 42,
    "qux-lorem": true
};

var object2 = {
    'foo': 'bar',
        
baz: 42
};

incorrect

Examples of correct code for this rule with the "consistent" option:

/*eslint @stylistic/js/quote-props: ["error", "consistent"]*/

var object1 = {
    "foo": "bar",
    "baz": 42,
    "qux-lorem": true
};

var object2 = {
    'foo': 'bar',
    'baz': 42
};

var object3 = {
    foo: 'bar',
    baz: 42
};

correct

consistent-as-needed

Examples of incorrect code for this rule with the "consistent-as-needed" option:

/*eslint @stylistic/js/quote-props: ["error", "consistent-as-needed"]*/

var object1 = {
        
foo: "bar"
,
    "baz": 42,
    "qux-lorem": true
};

var object2 = {
        
'foo': 'bar'
,
        
'baz': 42
};

incorrect

Examples of correct code for this rule with the "consistent-as-needed" option:

/*eslint @stylistic/js/quote-props: ["error", "consistent-as-needed"]*/

var object1 = {
    "foo": "bar",
    "baz": 42,
    "qux-lorem": true
};

var object2 = {
    foo: 'bar',
    baz: 42
};

correct

keywords

Examples of additional incorrect code for this rule with the "as-needed", { "keywords": true } options:

/*eslint @stylistic/js/quote-props: ["error", "as-needed", { "keywords": true }]*/

var x = {
        
while: 1
,
        
volatile: "foo"
};

incorrect

Examples of additional incorrect code for this rule with the "consistent-as-needed", { "keywords": true } options:

/*eslint @stylistic/js/quote-props: ["error", "consistent-as-needed", { "keywords": true }]*/

var x = {
        
"prop": 1
,
        
"bar": "foo"
};

incorrect

unnecessary

Examples of additional correct code for this rule with the "as-needed", { "unnecessary": false } options:

/*eslint @stylistic/js/quote-props: ["error", "as-needed", { "keywords": true, "unnecessary": false }]*/

var x = {
    "while": 1,
    "foo": "bar"  // Would normally have caused a warning
};

correct

numbers

Examples of additional incorrect code for this rule with the "as-needed", { "numbers": true } options:

/*eslint @stylistic/js/quote-props: ["error", "as-needed", { "numbers": true }]*/

var x = {
        
100: 1
}

incorrect

When Not To Use It

If you don't care if property names are consistently wrapped in quotes or not, and you don't target legacy ES3 environments, turn this rule off.