no-unexpected-multiline

Disallows confusing multiline expressions.

Semicolons are usually optional in JavaScript, because of automatic semicolon insertion (ASI). You can require or disallow semicolons with the semi rule.

The rules for ASI are relatively straightforward: As once described by Isaac Schlueter, a newline character always ends a statement, just like a semicolon, except where one of the following is true:

In the exceptions where a newline does not end a statement, a typing mistake to omit a semicolon causes two unrelated consecutive lines to be interpreted as one expression. Especially for a coding style without semicolons, readers might overlook the mistake. Although syntactically correct, the code might throw exceptions when it is executed.

Rule Details

This rule disallows confusing multiline expressions where a newline looks like it is ending a statement, but is not.

Examples of incorrect code for this rule:

/*eslint no-unexpected-multiline: "error"*/

var foo = bar
(1 || 2).baz();

var hello = 'world'
[1, 2, 3].forEach(addNumber);

let x = function() {}
`hello`

let x = function() {}
x
`hello`

let x = foo
/regex/g.test(bar)

Examples of correct code for this rule:

/*eslint no-unexpected-multiline: "error"*/

var foo = bar;
(1 || 2).baz();

var foo = bar
;(1 || 2).baz()

var hello = 'world';
[1, 2, 3].forEach(addNumber);

var hello = 'world'
void [1, 2, 3].forEach(addNumber);

let x = function() {};
`hello`

let tag = function() {}
tag `hello`

When Not To Use It

You can turn this rule off if you are confident that you will not accidentally introduce code like this.

Note that the patterns considered problems are not flagged by the semi rule.

Version

This rule was introduced in ESLint 0.24.0.

Resources