string.prototype.iswellformed 
An ESnext spec-compliant String.prototype.isWellFormed shim/polyfill/replacement that works as far down as ES3.
This package implements the es-shim API interface. It works in an ES3-supported environment and complies with the expected ES2024 spec.
Because String.prototype.isWellFormed depends on a receiver (the this value), the main export takes the string to operate on as the first argument.
Getting started
npm install --save string.prototype.iswellformedUsage/Examples
var isWellFormed = require('string.prototype.iswellformed');
var assert = require('assert');
var leadingPoo = '\uD83D';
var trailingPoo = '\uDCA9';
var wholePoo = leadingPoo + trailingPoo;
assert.ok(isWellFormed(wholePoo));
assert.notOk(isWellFormed(leadingPoo));
assert.notOk(isWellFormed(trailingPoo));var isWellFormed = require('string.prototype.iswellformed');
var assert = require('assert');
/* when String#isWellFormed is not present */
delete String.prototype.isWellFormed;
var shimmed = isWellFormed.shim();
assert.equal(shimmed, isWellFormed.getPolyfill());
assert.deepEqual(wholePoo.isWellFormed(), isWellFormed(wholePoo));var isWellFormed = require('string.prototype.iswellformed');
var assert = require('assert');
/* when String#at is present */
var shimmed = isWellFormed.shim();
assert.equal(shimmed, String.prototype.isWellFormed);
assert.deepEqual(wholePoo.isWellFormed(), isWellFormed(wholePoo));Tests
Simply clone the repo, npm install, and run npm test
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