Replacement for javascript escape?

Question

I know that the escape function has been deprecated and that you should use encodeURI or encodeURIComponent instead. However, the encodeUri and encodeUriComponent doesn't do the same thing as escape.

I want to create a mailto link in javascript with Swedish åäö. Here are a comparison between escape, encodeURIComponent and encodeURI:

Output:
mailto:?subject=My%20subject%20with%20%E5%E4%F6&body=My%20body%20with%20more%20characters%20and%20swedish%20%E5%E4%F6
mailto:?subject=My%20subject%20with%20%C3%A5%C3%A4%C3%B6&body=My%20body%20with%20more%20characters%20and%20swedish%20%C3%A5%C3%A4%C3%B6
mailto:?subject=My%20subject%20with%20%C3%A5%C3%A4%C3%B6&body=My%20body%20with%20more%20characters%20and%20swedish%20%C3%A5%C3%A4%C3%B6 

Only the mailto link created with "escape" opens a properly formatted mail in Outlook using IE or Chrome. When using encodeURI or encodeURIComponent the subject says:

My subject with åäö

and the body is also looking messed up.

Is there some other function besides escape that I can use to get the working mailto link?

Answer 1

escape() is defined in section B.2.1.2 escape and the introduction text of Annex B says:

... 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. ...

For characters, whose code unit value is 0xFF or less, escape() produces a two-digit escape sequence: %xx. This basically means, that escape() converts a string containing only characters from U+0000 to U+00FF to an percent-encoded string using the latin-1 encoding.

For characters with a greater code unit, the four-digit format %uxxxx is used. This is not allowed within the hfields section (where subject and body are stored) of an mailto:-URI (as defined in RFC6068):

mailtoURI    = "mailto:" [ to ] [ hfields ]
to           = addr-spec *("," addr-spec )
hfields      = "?" hfield *( "&" hfield )
hfield       = hfname "=" hfvalue
hfname       = *qchar
hfvalue      = *qchar
...
qchar        = unreserved / pct-encoded / some-delims
some-delims  = "!" / "$" / "'" / "(" / ")" / "*"
               / "+" / "," / ";" / ":" / "@"

unreserved and pct-encoded are defined in STD66:

unreserved  = ALPHA / DIGIT / "-" / "." / "_" / "~"
pct-encoded   = "%" HEXDIG HEXDIG

A percent sign is only allowed if it is directly followed by two hexdigits, percent followed by u is not allowed.

Using a self-implemented version, that behaves exactly like escape doesn't solve anything - instead just continue to use escape, it won't be removed anytime soon.

---

To summerise: Your previous usage of escape() generated latin1-percent-encoded mailto-URIs if all characters are in the range U+0000 to U+00FF, otherwise an invalid URI was generated (which might still be correctly interpreted by some applications, if they had javascript-encode/decode compatibility in mind).

It is more correct (no risk of creating invalid URIs) and future-proof, to generate UTF8-percent-encoded mailto-URIs using encodeURIComponent() (don't use encodeURI(), it does not escape ?, /, ...). RFC6068 requires usage of UTF-8 in many places (but allows other encodings for "MIME encoded words and for bodies in composed email messages").

Example:

text_latin1="Swedish åäö"
text_other="Emoji 😎"

document.getElementById('escape-latin-1-link').href="mailto:?subject="+escape(text_latin1);
document.getElementById('escape-other-chars-link').href="mailto:?subject="+escape(text_other);
document.getElementById('utf8-link').href="mailto:?subject="+encodeURIComponent(text_latin1);
document.getElementById('utf8-other-chars-link').href="mailto:?subject="+encodeURIComponent(text_other);

function mime_word(text){
  q_encoded = encodeURIComponent(text) //to utf8 percent encoded
  .replace(/[_!'()*]/g, function(c){return '%'+c.charCodeAt(0).toString(16).toUpperCase();})// encode some more chars as utf8
  .replace(/%20/g,'_') // mime Q-encoding is using underscore as space
  .replace(/%/g,'='); //mime Q-encoding uses equal instead of percent
  return encodeURIComponent('=?utf-8?Q?'+q_encoded+'?=');//add mime word stuff and escape for uri
}

//don't use mime_word for body!!!
document.getElementById('mime-word-link').href="mailto:?subject="+mime_word(text_latin1);
document.getElementById('mime-word-other-chars-link').href="mailto:?subject="+mime_word(text_other);

<a id="escape-latin-1-link">escape()-latin1</a><br/>
<a id="escape-other-chars-link">escape()-emoji</a><br/>
<a id="utf8-link">utf8</a><br/>
<a id="utf8-other-chars-link">utf8-emoji</a><br/>
<a id="mime-word-link">mime-word</a><br/>
<a id="mime-word-other-chars-link">mime-word-emoji</a><br/>

For me, the UTF-8 links and the Mime-Word links work in Thunderbird. Only the plain UTF-8 links work in Windows 10 builtin Mailapp and my up-to-date version of Outlook.