BEM helper

createBEM.js

import _ from 'lodash';

function objectToArray(object) {
  let keys   = Object.keys(object);
  let output = [];

  keys.forEach(function(key) {
    let predicate = object[key];

    if (_.isFunction(predicate)) {
      predicate = predicate();
    }

    if (predicate) {
      output.push(key);
    }
  });

  return output;
}

function listToArray(list) {
  if (_.isString(list) && list !== '') {
    return list.split(' ');
  } else if (list && list.length) {
    return list;
  } else if (_.isObject(list)) {
    return objectToArray(list);
  } else {
    return [];
  }
}

export default function createBEM(options) {
  if (_.isString(options)) {
    options = { name: options };
  }

  return function(first, modifiers) {
    let prefix       = options.prefix || 'b-';
    let rootName     = options.block;
    let classNames   = [];
    let element;

    // This means the first parameter is not the element, but a configuration letiable
    if (_.isObject(first)) {
      element = first.element;
      modifiers = first.modifiers || first.modifier;
    } else {
      element = first;
    }

    if (element) {
      rootName += '__' + element;
    }

    classNames.push(rootName);

    // Compose an array of modifiers
    listToArray(modifiers).forEach(function(modifier) {
      classNames.push(rootName + '--' + modifier);
    });

    // Add a prefix to all the classes in the classNames array
    for (let i = 0; i < classNames.length; i++) {
      classNames[i] = prefix + classNames[i];
    }

    return classNames.join(' ').trim();
  };
}