index.js

import * as esprima from 'esprima';

export default function extract(content) {
    const tokens = esprima.tokenize(content);
    let selectors = tokens
        .filter(token => {
            return (
                token.type === 'Identifier' ||
                token.type === 'Template' ||
                token.type === 'String'
            );
        })
        .reduce((acc, token) => {
            if (token.type === 'String') {
                // cut single/double quotes from the string
                // because esprima wraps string to a string
                const unwrappedString = token.value.slice(
                    1,
                    token.value.length - 1
                );
                return acc.concat(unwrappedString.split(' ')); // in case if string contains a list of classes
            } else if (token.type === 'Template') {
                // cut backticks from the template
                const len = token.value.length;
                const isOpenedTemplate = token.value[0] === '`';
                const isClosedTemplate = token.value[len - 1] === '`';
                const unwrappedTemplate = token.value.slice(
                    isOpenedTemplate ? 1 : 0,
                    isClosedTemplate ? len - 1 : len
                );
                return acc.concat(unwrappedTemplate.split(' '));
            }
            return acc.concat(token.value);
        }, []);

    // clear selectors from empty strings
    selectors = selectors.filter(selector => selector !== '');
    return [...new Set(selectors)]; // remove duplicates
}