Bem utils for Javascript/Typescript

bem.js

'use strict';

// Creates an array of truthy elements
const joinTruthy = (glue, ...args) => args.filter(arg => arg).join(glue);

// Simple bem function
export const bemUnbound = (blockName, elementName, options = {}) => [
  joinTruthy('__', blockName, elementName),
  ...Object
    .entries(options)
    .reduce(
      (classes, [key, enabled]) => enabled
        ? [
          ...classes,
          [joinTruthy('__', blockName, elementName), key].join('--')
        ]
        : classes, []
    )
].join(' ');

// The bem function which takes BLOCK_CLASS from the prototype
export const bem = function (elementName, options) {
  return bemUnbound(this.BLOCK_CLASS, elementName, options);
}


// Decorator function
export const EnableBem = (blockClass) =>
  (target) => {
    target.prototype.BLOCK_CLASS = blockClass;
    target.prototype.bem = bem;
  }