String.AsMultiline

Main.ts

declare global {
	interface String {
		/**
		 * Reformats a multi-line string to represent the actual intended "block" of text.
		 * @param desiredIndent How much to indent each line. (after removal of the first-line indent-length from each of them)
		 */
		AsMultiline(desiredIndent: number): string;
	}
}
String.prototype.AsMultiline = function(this: string, desiredIndent: number = null) {
	let result = this.substring(this.indexOf("\n") + 1, this.lastIndexOf("\n"));
	if (desiredIndent != null) {
		let lines = result.split("\n");
		let firstLineIndent = result.match(/^(\t+)/)?.[1].length ?? 0;
		if (firstLineIndent) {
			// remove X tabs from start of each line (where X is firstLineIndent)
			lines = lines.map(line=>line.replace(new RegExp(`^\t{0,${firstLineIndent}}`), ""));
		}
		// add the desired indent
		lines = lines.map(line=>"\t".repeat(desiredIndent) + line);
		result = lines.join("\n");
	}
	return result;
};

// usage example
// ==========

return (
	<Text>{`
		This is the first line.
		This is the second line.
		The resulting string will not contain any indent, since it's passed through the AsMultiline post-processor.
	`.AsMultiline(0)}</Text>
);