index.js

import sliceAnsi from 'slice-ansi';
import stringWidth from 'string-width';

function getIndexOfNearestSpace(string, wantedIndex, shouldSearchRight) {
	if (string.charAt(wantedIndex) === ' ') {
		return wantedIndex;
	}

	const direction = shouldSearchRight ? 1 : -1;

	for (let index = 0; index <= 3; index++) {
		const finalIndex = wantedIndex + (index * direction);
		if (string.charAt(finalIndex) === ' ') {
			return finalIndex;
		}
	}

	return wantedIndex;
}

export default function cliTruncate(text, columns, options = {}) {
	const {
		position = 'end',
		space = false,
		preferTruncationOnSpace = false,
	} = options;

	let {truncationCharacter = '…'} = options;

	if (typeof text !== 'string') {
		throw new TypeError(`Expected \`input\` to be a string, got ${typeof text}`);
	}

	if (typeof columns !== 'number') {
		throw new TypeError(`Expected \`columns\` to be a number, got ${typeof columns}`);
	}

	if (columns < 1) {
		return '';
	}

	if (columns === 1) {
		return truncationCharacter;
	}

	const length = stringWidth(text);

	if (length <= columns) {
		return text;
	}

	if (position === 'start') {
		if (preferTruncationOnSpace) {
			const nearestSpace = getIndexOfNearestSpace(text, length - columns + 1, true);
			return truncationCharacter + sliceAnsi(text, nearestSpace, length).trim();
		}

		if (space === true) {
			truncationCharacter += ' ';
		}

		return truncationCharacter + sliceAnsi(text, length - columns + stringWidth(truncationCharacter), length);
	}

	if (position === 'middle') {
		if (space === true) {
			truncationCharacter = ` ${truncationCharacter} `;
		}

		const half = Math.floor(columns / 2);

		if (preferTruncationOnSpace) {
			const spaceNearFirstBreakPoint = getIndexOfNearestSpace(text, half);
			const spaceNearSecondBreakPoint = getIndexOfNearestSpace(text, length - (columns - half) + 1, true);
			return sliceAnsi(text, 0, spaceNearFirstBreakPoint) + truncationCharacter + sliceAnsi(text, spaceNearSecondBreakPoint, length).trim();
		}

		return (
			sliceAnsi(text, 0, half)
				+ truncationCharacter
				+ sliceAnsi(text, length - (columns - half) + stringWidth(truncationCharacter), length)
		);
	}

	if (position === 'end') {
		if (preferTruncationOnSpace) {
			const nearestSpace = getIndexOfNearestSpace(text, columns - 1);
			return sliceAnsi(text, 0, nearestSpace) + truncationCharacter;
		}

		if (space === true) {
			truncationCharacter = ` ${truncationCharacter}`;
		}

		return sliceAnsi(text, 0, columns - stringWidth(truncationCharacter)) + truncationCharacter;
	}

	throw new Error(`Expected \`options.position\` to be either \`start\`, \`middle\` or \`end\`, got ${position}`);
}