Breakpoint helper in TypeScript

Breakpoint.ts

export enum Breakpoint {
  sm = 640,
  md = 768,
  lg = 1024,
  xl = 1080,
}

BreakpointHelper.ts

import _ from 'lodash';
import { Breakpoint } from './Breakpoint';
export { Breakpoint };

/**
 * A helper for using breakpoints.
 *
 * @class Breakpoint
 */
export default class BreakpointHelper {
  /**
   * Array of breakpoints.
   *
   * @private
   * @static
   * @returns {Array<Number>}
   * @memberof BreakpointHelper
   */
  static get breakpoints(): Array<Number> {
    return Object.values(Breakpoint)
      .filter(value => isNaN(Number(value)) === false)
      .map(key => Number(key));
  }

  /**
   * Gets the width of the document.
   */
  static getWidth(): Number {
    return window.innerWidth || document.documentElement.clientWidth || document.getElementsByTagName('body')[0].clientWidth;
  }

  /**
   * Gets the breakpoint above the current width.
   *
   * @static
   * @param {Number} [width]
   * @returns {(Breakpoint | null)}
   * @memberof BreakpointHelper
   */
  static up(width?: Number): Breakpoint | null {
    width = width || this.getWidth();

    let above: Number | null = _.find(this.breakpoints, (match: Number) => {
      let below = this.breakpoints[this.breakpoints.indexOf(match) - 1];
      return width <= match && (width > below || !below);
    });

    return above ? Breakpoint[(<Number>above).toString()] : null;
  }
  
  /**
   * Gets the breakpoint below the current width.
   *
   * @static
   * @param {Number} [width]
   * @returns {(Breakpoint | null)}
   * @memberof BreakpointHelper
   */
  static down(width?: Number): Breakpoint | null {
    width = width || this.getWidth();

    let below: Number | null = _.find(this.breakpoints, (match: Number) => {
      let above = this.breakpoints[this.breakpoints.indexOf(match) + 1];
      return width >= match && (width < above || !above);
    });

    return below ? Breakpoint[(<Number>below).toString()] : null;
  }

  /**
   * Checks if the current width is above the given breakpoint.
   *
   * @static
   * @param {Breakpoint} breakpoint
   * @param {Number} [width]
   * @returns
   * @memberof BreakpointHelper
   */
  static isAbove(breakpoint: Breakpoint, width?: Number) {
    return (width || this.getWidth()) > breakpoint;
  }

  /**
   * Checks if the current width is below the given breakpoint.
   *
   * @static
   * @param {Breakpoint} breakpoint
   * @param {Number} [width]
   * @returns
   * @memberof BreakpointHelper
   */
  static isBelow(breakpoint: Breakpoint, width?: Number) {
    return (width || this.getWidth()) < breakpoint;}
}