Algorithm to pad string is not Unicode aware

[kgryte]

Checklist

Please ensure the following tasks are completed before filing a bug report.

• Read and understood the Code of Conduct.
• Searched for existing issues and pull requests.

Description

Description of the issue.

Encountered an error when attempting to pad a string based on the number of visual characters. Currently, we rely on String#length to determine the number of characters to pad; however, this returns the number of code points, which may not be same as the number of graphemes.

We should consider how to properly handle Unicode characters comprised of multiple code points.

Related Issues

Does this issue have any related issues?

No.

Questions

Any questions for reviewers?

No.

Other

Any other information relevant to this issue? This may include screenshots, references, stack traces, sample output, and/or implementation notes.

This affects the following packages:

• @stdlib/string/left-pad
• @stdlib/string/right-pad
• @stdlib/string/pad

Demo

If relevant, provide a link to a live demo.

N/A

Reproduction

What steps are required to reproduce the unexpected output?

In order to reproduce this bug, do the following:

• attempt to pad using an input string containing surrogate pairs or by providing a string with which to pad containing surrogate pairs.

Expected Results

What are the expected results?

I might expect that I would see padding based on the number of visual characters. Currently, the implementation runs the risk of unpaired surrogates.

Actual Results

What are the actual results?

N/A

Environments

What environments are affected (e.g., Node v0.4.x, Chrome, IE 11)? If Node.js, include the npm version, operating system, and any other potentially relevant platform information.

The following environments are affected:

• all