nonblock-statement-body-position

Enforce the location of single-line statements

When writing if, else, while, do-while, and for statements, the body can be a single statement instead of a block. It can be useful to enforce a consistent location for these single statements.

For example, some developers avoid writing code like this:

if (foo)
  bar();

If another developer attempts to add baz(); to the if statement, they might mistakenly change the code to

if (foo)
  bar();
  baz(); // this line is not in the `if` statement!

To avoid this issue, one might require all single-line if statements to appear directly after the conditional, without a linebreak:

if (foo) bar();

Rule Details

This rule aims to enforce a consistent location for single-line statements.

Note that this rule does not enforce the usage of single-line statements in general. If you would like to disallow single-line statements, use the curly rule instead.

Options

This rule accepts a string option:

• "beside" (default) disallows a newline before a single-line statement.
• "below" requires a newline before a single-line statement.
• "any" does not enforce the position of a single-line statement.

Additionally, the rule accepts an optional object option with an "overrides" key. This can be used to specify a location for particular statements that override the default. For example:

• "beside", { "overrides": { "while": "below" } } requires all single-line statements to appear on the same line as their parent, unless the parent is a while statement, in which case the single-line statement must not be on the same line.
• "below", { "overrides": { "do": "any" } } disallows all single-line statements from appearing on the same line as their parent, unless the parent is a do-while statement, in which case the position of the single-line statement is not enforced.

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

/* eslint nonblock-statement-body-position: ["error", "beside"] */

if (foo)
  bar();
else
  baz();

while (foo)
  bar();

for (let i = 1; i < foo; i++)
  bar();

do
  bar();
while (foo)

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

/* eslint nonblock-statement-body-position: ["error", "beside"] */

if (foo) bar();
else baz();

while (foo) bar();

for (let i = 1; i < foo; i++) bar();

do bar(); while (foo)

if (foo) { // block statements are always allowed with this rule
  bar();
} else {
  baz();
}

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

/* eslint nonblock-statement-body-position: ["error", "below"] */

if (foo) bar();
else baz();

while (foo) bar();

for (let i = 1; i < foo; i++) bar();

do bar(); while (foo)

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

/* eslint nonblock-statement-body-position: ["error", "below"] */

if (foo)
  bar();
else
  baz();

while (foo)
  bar();

for (let i = 1; i < foo; i++)
  bar();

do
  bar();
while (foo)

if (foo) {
  // Although the second `if` statement is on the same line as the `else`, this is a very common
  // pattern, so it's not checked by this rule.
} else if (bar) {
}

Examples of incorrect code for this rule with the "beside", { "overrides": { "while": "below" } } rule:

/* eslint nonblock-statement-body-position: ["error", "beside", { "overrides": { "while": "below" } }] */

if (foo)
  bar();

while (foo) bar();

Examples of correct code for this rule with the "beside", { "overrides": { "while": "below" } } rule:

/* eslint nonblock-statement-body-position: ["error", "beside", { "overrides": { "while": "below" } }] */

if (foo) bar();

while (foo)
  bar();

When Not To Use It

If you’re not concerned about consistent locations of single-line statements, you should not turn on this rule. You can also disable this rule if you’re using the "all" option for the curly rule, because this will disallow single-line statements entirely.

Version

This rule was introduced in ESLint v3.17.0.

Further Reading

Resources

• Rule source
• Tests source