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eb39fafa4f
includes a (minimal) working wrapper Signed-off-by: Dominik Csapak <d.csapak@proxmox.com>
75 lines
2.3 KiB
Markdown
75 lines
2.3 KiB
Markdown
# disallow confusing multiline expressions (no-unexpected-multiline)
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Semicolons are usually optional in JavaScript, because of automatic semicolon insertion (ASI). You can require or disallow semicolons with the [semi](./semi.md) rule.
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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:
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* The statement has an unclosed paren, array literal, or object literal or ends in some other way that is not a valid way to end a statement. (For instance, ending with `.` or `,`.)
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* The line is `--` or `++` (in which case it will decrement/increment the next token.)
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* It is a `for()`, `while()`, `do`, `if()`, or `else`, and there is no `{`
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* The next line starts with `[`, `(`, `+`, `*`, `/`, `-`, `,`, `.`, or some other binary operator that can only be found between two tokens in a single expression.
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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.
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## Rule Details
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This rule disallows confusing multiline expressions where a newline looks like it is ending a statement, but is not.
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Examples of **incorrect** code for this rule:
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```js
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/*eslint no-unexpected-multiline: "error"*/
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var foo = bar
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(1 || 2).baz();
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var hello = 'world'
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[1, 2, 3].forEach(addNumber);
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let x = function() {}
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`hello`
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let x = function() {}
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x
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`hello`
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let x = foo
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/regex/g.test(bar)
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```
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Examples of **correct** code for this rule:
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```js
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/*eslint no-unexpected-multiline: "error"*/
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var foo = bar;
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(1 || 2).baz();
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var foo = bar
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;(1 || 2).baz()
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var hello = 'world';
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[1, 2, 3].forEach(addNumber);
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var hello = 'world'
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void [1, 2, 3].forEach(addNumber);
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let x = function() {};
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`hello`
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let tag = function() {}
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tag `hello`
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```
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## When Not To Use It
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You can turn this rule off if you are confident that you will not accidentally introduce code like this.
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Note that the patterns considered problems are **not** flagged by the [semi](semi.md) rule.
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## Related Rules
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* [func-call-spacing](func-call-spacing.md)
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* [semi](semi.md)
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* [space-unary-ops](space-unary-ops.md)
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