string-character-is-astral-surrogate^1.11.0

Tells, is given character a part of astral character, specifically, a high and low surrogate

Install via npm

npm i string-character-is-astral-surrogate

Consume via a require():

const { isHighSurrogate, isLowSurrogate } = require("string-character-is-astral-surrogate");

or as an ES Module:

import { isHighSurrogate, isLowSurrogate } from "string-character-is-astral-surrogate";

Install as a script, via CDN

Put this in your HTML:

<script src="https://cdn.jsdelivr.net/npm/string-character-is-astral-surrogate/dist/string-character-is-astral-surrogate.umd.js">

Then, you’ll get a global variable stringCharacterIsAstralSurrogate in your Global object and you consume it like this:

const { isHighSurrogate, isLowSurrogate } = stringCharacterIsAstralSurrogate;

Trivia

This program has 23 assertions in its unit tests. That's less than all unit test assertions' median (50) and less than geometric mean (70).

In monorepo, one other package, string-match-left-right, consumes this package.

§ Quick Take

import { strict as assert } from "assert";
import {
  isHighSurrogate,
  isLowSurrogate,
} from "string-character-is-astral-surrogate";

// 🧢 = \uD83E\uDDE2

assert.equal(isHighSurrogate("\uD83E"), true);
// the first character, high surrogate of the cap is indeed a high surrogate

assert.equal(isHighSurrogate("\uDDE2"), false);
// the second character, low surrogate of the cap is NOT a high surrogate

assert.equal(isLowSurrogate("\uD83E"), false);
// the first character, high surrogate of the cap is NOT a low surrogate
// it's a high surrogate

assert.equal(isLowSurrogate("\uDDE2"), true);
// the second character, low surrogate of the cap is indeed a low surrogate

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§ Idea

This program identifies high and low surrogates, specifically.

The API comprises of two functions:

isHighSurrogate (char)

isLowSurrogate (char)

It reads the character at first index (the first Unicode code point) and evaluates its charcode. That's it. If there are more characters they are ignored.

In theory, high surrogate goes first, low surrogate goes second source . This program enables us to detect surrogate-related errors, for example, malformed emoji or parts of emoji.

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§ API

Two functions, same API:

isHighSurrogate(str)

isLowSurrogate(str)

Input: zero or more characters, where charCodeAt(0) will be evaluated. Output: Boolean

If input is empty string or undefined, false is returned.
If input is anything other than the string or undefined, type error is thrown.
If input consists of more characters, everything beyond .charCodeAt(0) is ignored.

We return false to make life easier when traversing the string. When you check "next" character, if it doesn't exist, as far as astral-ness is concerned, we're fine, so it yields false. Otherwise, you'd have to check the input before feeding into this library and that's is tedious. This is a low-level library and it doesn't have to be picky.

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