php - JavaScript function call interprets encoded Single Quote %27 as literal

Question

Requirements:

• I have to fetch a URL that contains a single quote.
• I am required to call a function via; e.g. <a href="javascript:my_function('my_quote%27s.txt');">...</a>.

After a lot of hassle of trying to properly encode a single quote (%27) both Waterfox and Chrome both keep throwing errors. Chrome allowed me to see that the error was triggered because the browsers are taking it upon themselves to decode strings (when I have not programed them to) turning %27 in to the literal single quote character so it errors out before the function is even called (e.g. my_function('my_quotes's.txt') with the quote being internally decoded and causing the obvious triple quote issue).

I could use PHP's htmlentities($file_name, ENT_QUOTES) though I'd have to string replace ' which seems pointlessly convoluted.

• I am required to support the single quote and make the call via javascript:.
• I'd like to avoid literal interpretation of encoded strings when calling functions.
• I'd like to minimize the fuss and just use an encoding that JavaScript won't complain about.
• No frameworks or libraries.

How do I properly encode a single quote in a manner that JavaScript won't take it upon itself to somehow internally decode it and throw errors?

Answer 1

I am required to make the call via javascript:

Shudder. Please fix this. It's known as a bad practice since over ten years! And it's exactly what's causing the URI decoding - the javascript: schema is followed by an percent-encoded value to interpret.

So if you start with the js code

my_function('my&quote's.txt');

it would become one of

javascript:my_function%28%27my%26quote%27s.txt%27%29%3B
javascript:my_function(%27my%26quote%27s.txt%27)%3B
javascript:my_function('my%26quote's.txt')%3B

(the apostrophe ' and the parenthesis actually don't need to be encoded).

But 'my_quote's.txt' is not the valid javascript that you want to start with. What you're actually looking for is 'my_quote's.txt' or "my_quote's.txt'. To use these in a javascript:-scheme URI, it becomes

javascript:my_function('my_quote's.txt')%3B
javascript:my_function("my_quote's.txt")%3B

So if you generate this href string from a dynamic filename value, you must

1. String-escape the filename in the JS string literal
2. URL-encode the complete code in the javascript url
3. html-entity-escape the complete href attribute value