html comments are valid in JS about acorn HOT 12 CLOSED

It was discussed some time back in UglifyJS too. My decision was to not support such comment style.

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@mishoo Why?

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Found it by Google: mishoo/UglifyJS#346

@mathiasbynens I might reconsider if there's enough interest, but right now I feel it's uselessly complicating the lexer.

Edit: @getify — nope, your example doesn't make me change my mind… should it?

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[edit: moving my uglifyjs questions to the uglifyjs repo :)]

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@getify my decision is based on the fact that ES5 doesn't define such comment format, and the syntax of this language is already awfully complex. Every little thing, no matter how insignificant, just adds to the mess. I don't even wanna think about parsing ES6 yet… :-(

But we're discussing this on Acorn's issue tracker. Let's see what @marijnh has to say. :-) If he decides to implement it in Acorn, that'll weight more for me than “popular demand”.

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It's apparently slated to standardize in ES6: http://people.mozilla.org/~jorendorff/es6-draft.html#sec-B.1.3

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Can anyone give some background on where this bizarre convention came from? A bug that was canonized as standard? Treating <!-- to --> as a block comment, I could understand, but treating both as line comment markers is just... crazy.

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treating both as line comment markers is just... crazy.

I concur on that feeling. The reason must be that --> is encountered frequently as a valid construct, i.e. while (x-->0) … so a block comment would end in the wrong place anyway. But this kinda makes the whole thing a nonsense.

Any case, I implemented it in UglifyJS2. The fact that V8 supports the syntax is too strong a reason...

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@marijnh because really old browsers (Netscape 1.0 I think) didn't understand <script> tags, and at the time, this was the only way to get JS to work in the "modern" browsers while still supporting the "older" ones.

What I don't understand is why it needed to be supported in any context besides a <script> tag - but since it is…

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Note that --> is only a line comment marker if it is the first thing on the line, optionally preceded by only whitespace or multi-line comments.

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What I don't understand is why it needed to be supported in any context besides a <script> tag - but since it is…

Because doing so would needlessly complicate JavaScript engines even more.

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I guess it grew out of a very crude strategy to deal with the old hack of putting <!-- and --> around the content of script tags to deal with non-script-supporting browsers, then?

I think attached patch should solve the issue. Though I am still puzzled how anyone would still want to be relying on this behavior.

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