uate - ES5 "Tagged Template Strings"

(Pronounced "you ate" as in "evaluate"...)

var a = 1, b = 2; eval(uate( "${a} + ${b} = ${a + b}" )); // "1 + 2 = 3"

Usage

eval(uate( template ))

eval(uate( tag, template ))

template must be a string containing zero or more ${expr} clauses which are evaluated in the local scope.

tag is optional, and may either be a named function in scope or a string containing an expression that in the local scope will yield a function e.g. 'console.log'. The function is called as tag(strings, ...substitutions).

The built-in html function does HTML entity escaping of &<>"' in substitutions.

The built-in uri function applies encodeURIComponent to substitutions.

The built-in halfbaked function yields escaped strings.

Examples

var a = 1, b = 2; eval(uate( "${a} + ${b} = ${a + b}" )); // "1 + 2 = 3"

eval(uate( tag, "a${ 42 }b" )); // whatever tag wants

eval(uate( halfbaked, "a\n${42}b" )); // "a\\n42b"

eval(uate( html, "<p>${untrusted_data}</p>" )); // ampersands galore

eval(uate( url, "http://example.com?q=${search}" )); // percents galore

Tag Functions

A trivial tag function has this form:

function tag(strings /*, ...substitutions*/) {
  var substitutions = [].slice.call(arguments, 1);

  var result = strings[0];
  for (var i = 0; i < substitutions.length; ++i) {
    result += substitutions[i];
    result += strings[i + 1];
  }
  return result;
}

Although it is not very useful in this ES5 hack, strings.raw is another array containing escaped versions of the strings.

Inspiration

ES6 Tagged String Templates, designed by Mike Samuel, et. al.

In ES6 you can write:

var a = 1, b = 2; `${a} + ${b} = ${a + b}`; // "1 + 2 = 3"

tag`a${ 42 }b`; // whatever tag wants

String.raw`a\n${42}b`; // "a\\n42b"

safehtml`<p>${untrusted_data}</p>`; // ampersands galore, and more

While it's not obvious in these examples, in ES6 the tag function is able to access the "raw" (unescaped) string fragments which allows it to implement domain specific languages using its own rich syntax. This ES5 version is just a toy.

Tests

Tests are included - run them at: https://inexorabletash.github.io/uate/tests.html

References

• http://tc39wiki.calculist.org/es6/template-strings/
• http://wiki.ecmascript.org/doku.php?id=harmony:specification_drafts
• http://wiki.ecmascript.org/doku.php?id=harmony:quasis

Trivia

Call without eval() to understand how it works.

Here's a smaller (but less capable) version that fits in a tweet:

function uate(s){return(''+s).split(/\${(.*?)}/).map(function(p,i){
    return(i%2)?'('+p+')':JSON.stringify(p);}).join('+');}