feat(assignVar): Patch for assignVar to add "drop key" feature and fixes reflecting documentation

[34638a]

Proposal, What? Why?

Helper assignVar currently does not have a way to do any of the following features:

1. Un-Map a assigned value: once a key has been set, it is locked for the whole render pipeline. This results in features like widgets taking up half of the available variables only to use them once and never again, limiting theme developers from being able to add new features due to limited variable space.
2. Accept an empty string into a variable as its value. Given a string is valid input, all states of a string should be considered as valid, limited by length. For instance, if a variable is set to "" because it is intended to be a placeholder when a value is not provided by the store admins or a customer input, say for a phone number click to call, this will currently cause the store to err.500 instead of handling what should be a valid input. The data input is inherently reasonable, so there is a patch in the validation logic to accept an empty string value instead of rejecting it.
3. Ingest a SafeString object and treat it like a actual string for purposes of storage and retreival. Current workaround possible as per open issue assignVar helper does not work with SafeString #139

Changes Overview

Create patch for assignVar to add following features:

• Empty string ( "" ) to be accepted as entry into assignVar helper.
• Null or Undefined values as input to assignVar now delete the key that was set. This has the use-case of freeing variables assigned by widgets or temporary assignments.
• Internal conversion via unwrapSafeString call before variable is process to all for storage and retrieval of SafeString contents.
• Tests for these use-cases in assignVar-getVar.js

How was it tested?

Test cases provided in assignVar-getVar.js file.

---

cc @bigcommerce/storefront-team

[34638a]

Reference to open issue #305

[34638a]

Reference to open issue #139
^ This will need to be added as a part of the "string" type checks / validation logic.
Note for @34638a to add this into the next PR push for proposal.

[34638a]

Rename title of PR due to 100 character limit:
feat(assignVar): Patch for assignVar to add feature and amend function reflecting documentation / scope. feat(assignVar): Patch for assignVar to add "drop key" feature and fixes reflecting documentation.

[34638a]

Amended PR context header to reflect #139 issue.

[34638a]

Hey @jairo-bc

Clarification request: given the line comment in the actual code, this reads as incorrect implementation. Can you please confirm if the below code should be interpreted as "the buffer length of 1024 should contain no more than 1024", or as per the current implementation "the buffer cannot hold 1024 character, or more than 1024 characters. The limit is 1023 characters in the buffer."

        // Validate that string is not longer than the max length
        if (utils.isString(value) && value.length >= max_length) {
            throw new ValidationError(`assignVar helper value must be less than ${max_length} characters, 
                but a ${value.length} character value was set to ${key}`);
        }

• Jordan

[34638a]

@jairo-bc @bc-evan-johnson
Other than the above @ for clarification,
I think it's ready for review. Thoughts and feedback are appreciated.

• Jordan

[github-actions]

🎉 This PR is included in version 6.3.0 🎉

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• npm package (@latest dist-tag)
• v6.3.0

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