Template Literals

Are Broken

Template Literals

• should enable embedding languages
• but escape sequences introduce a problem
• \u00FF is a legal escape sequence but \unicode is not
• can't embed languages if syntax is restricted to legal ES escape sequences

function latex(strs) {
  // ...
}

let doc = latex`
\newcommand{\fun}{\textbf{Fun!}}
\newcommand{\unicode}{\textbf{Unicode!}} 
\newcommand{\xerxes}{\textbf{King!}} 

Breve over the h goes \u{h}ere 
`;

Proposal:

Remove escape sequence restriction

Cooked Values Option 1

• How should we handle cooked values with illegal escape sequences?
• Cook valid escape sequences and leave invalid escape sequences raw
• Seems like a footgun
• Could be surprising that \unicode is literal but \uface is cooked to 龜

function tag(strs) {
  strs[0] === "\\unicode and U"
  strs.raw[0] === "\\unicode and \\u{55}";
}
tag`\unicode and \u{55}`

Cooked Values Option 2

• How should we handle cooked values with illegal escape sequences?
• Set cooked values with illegal escape sequences to undefined
• Programmers still have access to raw

function tag(strs) {
  strs[0] === undefined
  strs.raw[0] === "\\unicode and \\u{55}";
}
tag`\unicode and \u{55}`