Beautification problem with JS Single Line Comment <!--

In Javascript <!-- is treated as a single-line comment just like //.

js-beautify works as expected when the line starts with <!--:

Input: <!--alert(1)commented

Output: <!--alert(1)commented

Otherwise it will break the syntax:

Input: alert(1)<!--commented

Output: alert(1) < !--commented

[Nowasky]

Please refer to annex B1.3 of the ES6 espec. https://www.ecma-international.org/ecma-262/11.0/index.html#prod-annexB-SingleLineHTMLOpenComment

B.1.3 HTML-like Comments

Comment:: MultiLineComment SingleLineComment SingleLineHTMLOpenComment SingleLineHTMLCloseComment SingleLineDelimitedComment

SingleLineHTMLOpenComment:: <!–SingleLineCommentCharsopt

Although it’s a legacy support as noted:

This annex describes various legacy features and other characteristics of web browser based ECMAScript implementations. All of the language features and behaviours specified in this annex have one or more undesirable characteristics and in the absence of legacy usage would be removed from this specification. However, the usage of these features by large numbers of existing web pages means that web browsers must continue to support them. The specifications in this annex define the requirements for interoperable implementations of these legacy features.

These features are not considered part of the core ECMAScript language. Programmers should not use or assume the existence of these features and behaviours when writing new ECMAScript code. ECMAScript implementations are discouraged from implementing these features unless the implementation is part of a web browser or is required to run the same legacy ECMAScript code that web browsers encounter.

[bitwiseman]

Switch to JavaScript beautification an try the example from the original description.

alert(1)<!--commented