The idea that you can “always use semicolons” and not worry about Automatic Semicolon Insertion (ASI) is completely incorrect.
Woops, you remembered to put a semicolon, but doesn’t matter. ASI kicked in and changed your code to:
So, it’s misleading to tell people that if they just “always use semicolons” their code is safe from surprising ASI behavior.
ASI will be with us forever. It’s about time you learned how it works. Not to worry: ASI is fully-specified in the ECMAScript language standard and all browsers implement it exactly the same way.
At the very least, consider using a linter that checks for unexpected ASI behavior. ESLint has a rule called
no-unexpected-multiline which catches unexpected ASI behavior. And once you’re using a linter, it doesn’t matter whether you use or omit semicolons since the linter keeps you safe.
The argument for “never use semicolons”
It’s not actually that simple to “always use semicolons”. There are actually many edge cases where you still aren’t supposed to use a semicolon! For example:
And what about these cases:
There are actually many more “edge cases” to keep in mind with “always use semicolons” than with “never use semicolons”.
If you “never use semicolons”, there’s only one rule: Never start a line with
In those cases, you simply prepend a
; like this:
However, if you frequently write code like this, you may be trying to be needlessly clever. This is actually much simpler:
And if you use a linter like
standard, then you don’t need to remember anything as unexpected ASI is reported as an error.
*The full list also includes some additional characters which would never actually appear at the start of an expression in real-world code:
- ESLint rule:
(If you liked this, you might like Cheating in Video Games.)