Fix substitution evaluation (fixes #143)

[fatfisz]

From the spec:

The string conversion semantics applied to the Expression value are like String.prototype.concat rather than the + operator.

Currently method processSubstitutions of TemplateTag is concatenating strings using the + operator, which results in the default hint while calling the abstract operation ToPrimitive. That causes valueOf to be called before toString if the value is an object. This is not in line with the spec and caused confusion (#143).

The fix is to simply use ''.concat (or call String on everything).

[codecov]

Codecov Report

Merging #144 into master will not change coverage.
The diff coverage is 100%.

@@          Coverage Diff          @@
##           master   #144   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files          24     24           
  Lines         102    102           
  Branches       29     29           
=====================================
  Hits          102    102

Impacted Files	Coverage Δ
src/TemplateTag/TemplateTag.js	100% <100%> (ø)	⬆️

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[inquisitivecrystal]

Any word on this? Having to manually call toString is pretty annoying.

[fatfisz]

I'll see what I can do after work today. It seems that @declandewet was unavailable for review (as you may have heard he is recovering from an accident).

[inquisitivecrystal]

I hadn't heard, am very sorry to hear that, and wish him a speedy recovery. In light of his unavailability, could you merge it on your own authority, as a collaborator?

[fatfisz]

I'll add one more thing before releasing the next version. Please give it at most 2 more days and it'll be published!