Stage 1 Draft / July 1, 2022

String.cooked

New API

This adds a builtin static method to String

1 Properties of the String Constructor 1

1.1 String.cooked ( template, ...substitutions )

The String.cooked function may be called with a variable number of arguments. The first argument is template and the remainder of the arguments form the List substitutions. The following steps are taken:

  1. Return ? InterpolateTemplateStringsArray(template, substitutions, cooked).
 Note

The cooked function implements behaviour suitable for a tag function of a Tagged Template (13.3.11). When called as such, the first argument will be a well formed template object and the rest parameter will contain the substitution values. In practice, it is more useful as a function which custom tag functions delegate to as a final step.

1.2 InterpolateTemplateStringsArray ( template, substitutions, prep )

The abstract operation InterpolateTemplateStringsArray takes arguments template (an ECMAScript language value), substitutions (a List of ECMAScript language values), and prep (cooked or raw) and returns either a normal completion containing a String or a throw completion. It performs the following steps when called:

  1. Let numberOfSubstitutions be the number of elements in substitutions.
  2. Let cooked be ? ToObject(template).
  3. If prep is cooked, let t be cooked; else let t be ? ToObject(? Get(cooked, "raw")).
  4. Let literalSegments be ? LengthOfArrayLike(t).
  5. If literalSegments ≤ 0, return the empty String.
  6. Let stringElements be a new empty List.
  7. Let nextIndex be 0.
  8. Repeat,
    1. Let nextKey be ! ToString(𝔽(nextIndex)).
    2. Let nextVal be ? Get(t, nextKey).
    3. If Type(nextVal) is Undefined, throw a TypeError exception.
    4. Let nextSeg be ? ToString(nextVal).
    5. Append the code unit elements of nextSeg to the end of stringElements.
    6. If nextIndex + 1 = literalSegments, then
      1. Return the String value whose code units are the elements in the List stringElements. If stringElements has no elements, the empty String is returned.
    7. If nextIndex < numberOfSubstitutions, let next be substitutions[nextIndex].
    8. Else, let next be the empty String.
    9. Let nextSub be ? ToString(next).
    10. Append the code unit elements of nextSub to the end of stringElements.
    11. Set nextIndex to nextIndex + 1.
 Editor's Note

This implements a generic abstract operation that can be reused by String.raw. When making the pull request into ecma262, we should update String.raw as well.

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© 2022 Darien Maillet Valentine

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