Never start a line with regular expression literal

[academyofzhuang]

If one start a line with a regular expression, it causes parsing error, too.

var s = 'About'
// if string begins with a Capital letter, print it
/^[A-Z].+/.test(s) && console.log(s)

Adding a semicolon before regex solved the problem.

Shall we add this exception to the rule.

[ifraixedes]

I don't understand what you meant.

Without semicolon, standard reports an error, because it's an actual syntax error, if you add a semicolon then the syntax is correct and standard doesn't report any error.

[dcousens]

@ifraixedes I think @academyofzhuang means these rules:

Never start a line with (, [, or `

[feross]

The list is intentionally incomplete. I listed only characters that have I've seen used in actual code, and ignored characters that are usually never used. A more complete list appears later in the rules in the quote from An Open Letter to JavaScript Leaders Regarding Semicolons:

The next line starts with [, (, +, *, /, -, ,, ., or some other binary operator that can only be found between two tokens in a single expression.

[dcousens]

@ifraixedes a better solution to your problem:

if (/^[A-Z].+/.test(s)) console.log(s)

I agree with @feross, this is a non-issue as the only use case I can see, is if you are doing what you were, which is never ideal IMHO.

[ifraixedes]

@dcousens I think that you ping the wrong person.

I have never written something how it was expressed in the question, I prefer forms as the one that you described above.

Cheers

[dcousens]

Apologies @ifraixedes, I meant @academyofzhuang

[academyofzhuang]

I agreed with you. Using boolean shortcut to save a few key strokes isn't best practice to start with.

The reason I brought up the issue is the parsing error message by js engine was cryptic:

standard: Use JavaScript Standard Style (http://standardjs.com)
  /Users/aoz/academyofzhuang/test/std.js:2:2: Parsing error: Unexpected token ^

When I look at the code, it doesn't make any sense.

var s = 'About'
/^[A-Z].+/.test(s) && console.log(s) // quick and dirty debug

Since I believed, as stated in the project readme

This is the only gotcha with omitting semicolons – automatically checked for you!

It took me some time to realize a semicolon might be needed.

I agree this is a non-issue. To quote the project readme:

Clever short-hands are discouraged, in favor of clear and readable expressions, whenever possible.

Thank you for the detailed explanation and example code!