enforce placing object properties on separate lines (object-property-newline)

The --fix option on the command line can automatically fix some of the problems reported by this rule.

This rule permits you to restrict the locations of property specifications in object literals. You may prohibit any part of any property specification from appearing on the same line as any part of any other property specification. You may make this prohibition absolute, or, by invoking an object option, you may allow an exception, permitting an object literal to have all parts of all of its property specifications on a single line.

Rule Details

Motivations

This rule makes it possible to ensure, as some style guides require, that property specifications appear on separate lines for better readability. For example, you can prohibit all of these:

const newObject = {a: 1, b: [2, {a: 3, b: 4}]};
const newObject = {
    a: 1, b: [2, {a: 3, b: 4}]
};
const newObject = {
    a: 1,
    b: [2, {a: 3, b: 4}]
};
const newObject = {
    a: 1,
    b: [
        2,
        {a: 3, b: 4}
    ]
};

Instead of those, you can comply with the rule by writing

const newObject = {
    a: 1,
    b: [2, {
        a: 3,
        b: 4
    }]
};

or

const newObject = {
    a: 1,
    b: [
        2,
        {
            a: 3,
            b: 4
        }
    ]
};

Another benefit of this rule is specificity of diffs when a property is changed:

// More specific
 var obj = {
     foo: "foo",
-    bar: "bar",
+    bar: "bazz",
     baz: "baz"
 };

// Less specific
-var obj = { foo: "foo", bar: "bar", baz: "baz" };
+var obj = { foo: "foo", bar: "bazz", baz: "baz" };

Optional Exception

The rule offers one object option, allowAllPropertiesOnSameLine (a deprecated synonym is allowMultiplePropertiesPerLine). If you set it to true, object literals such as the first two above, with all property specifications on the same line, will be permitted, but one like

const newObject = {
    a: 'a.m.', b: 'p.m.',
    c: 'daylight saving time'
};

will be prohibited, because two properties, but not all properties, appear on the same line.

Notations

This rule applies equally to all property specifications, regardless of notation, including:

• a: 1 (ES5)
• a (ES2015 shorthand property)
• [`prop${a}`] (ES2015 computed property name)

Thus, the rule (without the object option) prohibits both of these:

const newObject = {
    a: 1, [
        process.argv[4]
    ]: '01'
};
const newObject = {
    a: 1, [process.argv[4]]: '01'
};

(This behavior differs from that of the JSCS rule cited below, which does not treat the leading [ of a computed property name as part of that property specification. The JSCS rule prohibits the second of these formats but permits the first.)

Multiline Properties

The rule prohibits the colocation on any line of at least 1 character of one property specification with at least 1 character of any other property specification. For example, the rule prohibits

const newObject = {a: [
    'Officiële website van de Europese Unie',
    'Официален уебсайт на Европейския съюз'
], b: 2};

because 1 character of the specification of a (i.e. the trailing ] of its value) is on the same line as the specification of b.

The optional exception does not excuse this case, because the entire collection of property specifications spans 4 lines, not 1.

Inter-property Delimiters

The comma and any whitespace that delimit property specifications are not considered parts of them. Therefore, the rule permits both of these formats:

const newFunction = multiplier => ({
    a: 2 * multiplier,
    b: 4 * multiplier,
    c: 8 * multiplier
});
const newFunction = multiplier => ({
    a: 2 * multiplier
    , b: 4 * multiplier
    , c: 8 * multiplier
});

(This behavior differs from that of the JSCS rule cited below, which permits the first but prohibits the second format.)

–fix

If this rule is invoked with the command-line --fix option, object literals that violate the rule are generally modified to comply with it. The modification in each case is to move a property specification to the next line whenever there is part or all of a previous property specification on the same line. For example,

const newObject = {
    a: 'a.m.', b: 'p.m.',
    c: 'daylight saving time'
};

is converted to

const newObject = {
    a: 'a.m.',
b: 'p.m.',
    c: 'daylight saving time'
};

The modification does not depend on whether the object option is set to true. In other words, ESLint never collects all the property specifications onto a single line, even when the object option would permit that.

ESLint does not correct a violation of this rule if a comment immediately precedes the second or subsequent property specification on a line, since ESLint cannot determine which line to put the comment onto.

As illustrated above, the --fix option, applied to this rule, does not comply with other rules, such as indent, but, if those other rules are also in effect, the option applies them, too.

Examples

Examples of incorrect code for this rule, with no object option or with allowAllPropertiesOnSameLine set to false:

/*eslint object-property-newline: "error"*/

const obj0 = { foo: "foo", bar: "bar", baz: "baz" };

const obj1 = {
    foo: "foo", bar: "bar", baz: "baz"
};

const obj2 = {
    foo: "foo", bar: "bar",
    baz: "baz"
};

const obj3 = {
    [process.argv[3] ? "foo" : "bar"]: 0, baz: [
        1,
        2,
        4,
        8
    ]
};

const a = "antidisestablishmentarianistically";
const b = "yugoslavyalılaştırabildiklerimizdenmişsiniz";
const obj4 = {a, b};

const domain = process.argv[4];
const obj5 = {
    foo: "foo", [
    domain.includes(":") ? "complexdomain" : "simpledomain"
]: true};

Examples of correct code for this rule, with no object option or with allowAllPropertiesOnSameLine set to false:

/*eslint object-property-newline: "error"*/

const obj1 = {
    foo: "foo",
    bar: "bar",
    baz: "baz"
};

const obj2 = {
    foo: "foo"
    , bar: "bar"
    , baz: "baz"
};

const user = process.argv[2];
const obj3 = {
    user,
    [process.argv[3] ? "foo" : "bar"]: 0,
    baz: [
        1,
        2,
        4,
        8
    ]
};

Examples of additional correct code for this rule with the { "allowAllPropertiesOnSameLine": true } option:

/*eslint object-property-newline: ["error", { "allowAllPropertiesOnSameLine": true }]*/

const obj = { foo: "foo", bar: "bar", baz: "baz" };

const obj2 = {
    foo: "foo", bar: "bar", baz: "baz"
};
const user = process.argv[2];
const obj3 = {
    user, [process.argv[3] ? "foo" : "bar"]: 0, baz: [1, 2, 4, 8]
};

When Not To Use It

You can turn this rule off if you want to decide, case-by-case, whether to place property specifications on separate lines.

Compatibility

• JSCS: This rule provides partial compatibility with requireObjectKeysOnNewLine.

Related Rules

• brace-style
• comma-dangle
• key-spacing
• object-curly-spacing

Version

This rule was introduced in ESLint 2.10.0.

Resources

• Rule source
• Documentation source