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You do not need to write a semicolon after every JavaScript statement. ECMAScript allows many statement-ending semicolons to be omitted through automatic semicolon insertion (ASI). But ASI is governed by grammar rules—not a simple “newline means semicolon” rule—so certain line breaks can change how code is parsed. Use the formatter and lint configuration already adopted by your project, and learn the cases where line breaks matter.
What automatic semicolon insertion does
Ecma International’s ECMAScript 2026 Language Specification, §12.10 says, “Most ECMAScript statements and declarations must be terminated with a semicolon.” It immediately qualifies that rule: semicolons may be omitted from source text in specified situations. The specification defines when a semicolon is inserted into the token stream; it does not say that every newline closes a statement.
In broad terms, ASI can insert a semicolon when the next token cannot continue the current grammar production and a line terminator, closing brace, or end of input applies. It also applies at certain restricted line breaks, such as after return. There is an important exception: insertion does not happen if it would create an empty statement or become a separator in a for header.
What changes when you omit semicolons?
A newline after return ends the return statement
A line terminator immediately after return ends that statement. The object on the next line is not returned:
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function getValue() {
return
{ answer: 42 }
}This function returns undefined. Put the expression on the same line to return the object:
function getValue() {
return { answer: 42 }
}This is not fixed by adding semicolons elsewhere in a file: the relevant issue is the line break after return.
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A line starting with ( or [ can continue the previous expression
Without a statement-ending semicolon, a parenthesized expression on the next line may be parsed as a continuation of the previous expression. For example:
const settings = {}
(function () {
configure(settings)
})()The parenthesized function expression can be treated as a call on the preceding object, rather than as a separate statement. A line beginning with [ can cause a similar continuation. In semicolon-free code, a defensive leading semicolon makes the next expression independent:
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const settings = {}
;(function () {
configure(settings)
})()With an explicit-semicolon style, terminate the preceding statement instead.
Other line-sensitive syntax
ECMAScript has restricted productions in which a line terminator affects whether tokens belong to the same construct. Keep these together as appropriate:
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- Keep the expression on the same line as
return,throw, oryield. - Keep a label on the same line as
breakorcontinuewhen using a label. - Keep postfix
++or--with its operand. - Keep arrow-function parameters with
=>, and keepasyncwith the following function or method token.
Breaking these forms across lines can force semicolon insertion, change the result, or produce a syntax error. The specification’s ASI rules describe the relevant conditions.
Explicit semicolons versus omitting them
| Consideration | Explicit semicolons | No statement-ending semicolons |
|---|---|---|
| Statement boundaries | Make statement endings visible in the source. | Rely more on readers and tools understanding ASI’s grammar rules. |
| Punctuation | Add a visible mark at statement endings. | Reduce statement-ending punctuation. |
| Adjacent expressions | Terminating a statement helps prevent a following ( or [ from continuing it. |
May require a defensive semicolon at the start of a line that could continue the previous expression. |
| Line breaks after restricted keywords | Do not prevent a line break after return or other restricted forms from changing parsing. |
Also require care with these line breaks; omitting semicolons is not the cause of every ASI pitfall. |
| Consistency | Works best when the project’s formatter and lint rules agree. | Also works best when the project’s formatter and lint rules agree. |
Neither convention is universally more correct. The practical choice is a code-style and tooling decision; correctness depends on whether the source parses as intended. The cited language and tool documentation does not establish a runtime speed advantage for either style.
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How to enforce a consistent style
Prettier
Prettier documents semi: true as the default. Setting semi: false omits statement-ending semicolons but retains leading semicolons where needed to protect against ASI continuation hazards. See the Prettier semicolon option. Keep the formatter’s setting aligned with the conventions expected by the project.
ESLint
ESLint’s core semi rule documentation describes always and never styles and options for statement-continuation characters. The core rule was deprecated in ESLint v8.53.0; its documentation directs users to the corresponding rule in @stylistic/eslint-plugin. Check the project’s installed ESLint version and configuration before copying rule syntax. ESLint also documents no-unexpected-multiline as a way to disallow confusing multiline expressions.
JavaScript Standard Style
Standard Style’s semicolon rule omits statement-ending semicolons and uses a leading defensive semicolon where the next expression could otherwise continue the previous one. It is one established convention, not a requirement for JavaScript.
Which style should you use?
- Check the project’s existing configuration. Follow its formatter and lint rules rather than introducing a competing style.
- If you are setting a new convention, choose one policy. Decide whether statement-ending semicolons should be present, then configure the formatter and linter to agree.
- Review line breaks around restricted syntax. In particular, check expressions after
return,throw, oryield, and statement starts with(or[. - Let the tools catch drift. Run the project’s formatter and lint checks so changes do not leave files with mixed conventions or confusing multiline expressions.
Explicit semicolons make boundaries more visible; a semicolon-free convention can be equally workable when its formatter and lint policy are followed. In both styles, understanding the line breaks that affect parsing is more useful than relying on a blanket rule about newlines.
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