@vectara/vectara-ui/lib/utils/truncateString.js

Vectara's design system, codified as a React and Sass component library

export const truncateStart = (source, maxLength) => {
    if (source.length < maxLength || maxLength <= 0)
        return source;
    const truncatedSource = source.substring(source.length - maxLength, source.length).trim();
    if (truncatedSource.length)
        return `…${truncatedSource}`;
    return truncatedSource;
};
export const truncateEnd = (source, maxLength) => {
    if (source.length < maxLength || maxLength <= 0)
        return source;
    const truncatedSource = source.substring(0, maxLength).trim();
    if (truncatedSource.length) {
        if ([".", "?", "!"].includes(truncatedSource[truncatedSource.length - 1])) {
            return `${truncatedSource} …`;
        }
        return `${truncatedSource}…`;
    }
    return truncatedSource;
};