parse-font.js

const checkers = {
	isSize(value) {
		throw new Error('Not implemented');
	},
	isStyle(value) {
		throw new Error('Not implemented');
	},
	isVariant(value) {
		throw new Error('Not implemented');
	},
	isWeight(value) {
		throw new Error('Not implemented');
	},
	isStretch(value) {
		throw new Error('Not implemented');
	}
}

const result = {
	style: 'normal',
	variant: 'normal',
	weight: 'normal',
	stretch: 'normal',
	height: 'normal',
	warnings: [],
	errors: []
};

const preProps = ['style', 'variant', 'weight', 'stretch'];

module.exports = parseFont(value) {

	const tokens = value.split(/\s+/);
	
	for (const token = tokens.shift(); tokens.length; token = tokens.shift()) {
		
		if (token === 'normal') {
			continue;
		}

		if (token === 'inherit') {
			preProps.forEach(prop => {
				result[prop] = token;
			});
			continue;
		}

		if (checkers.isSize(token)) {
			const [ size, lineHeight ] = token.split('/');
			result.size = size;
			if (typeof lineHeight !== undefined) {
				result.lineHeight = lineHeight;
			}
			result.family = unquote(tokens);
			break;
		}

		preProps.forEach(prop => {
			if (checkers[`is${prop}`](token)) {
				result[prop] = token;
				continue;
			}
		});

		result.errors.push(new Error(`Unknown value: ${token}`));
	}

}