My personal, ongoing list of useful JavaScript prototype polyfills ¯\_(ツ)_/¯

polyfills.js

/**
 * String.capitalize - Capitalize the first character of a string.
 *
 * Example: 
 *   const foo = "this is a headline"
 *   foo.capitalize()
 *   This is a headline
 */
String.prototype.capitalize = function() {
  return this.charAt(0).toUpperCase() + this.slice(1);
};


/**
 * Array.chunk() - Break an array down into chunks
 *
 * Example:
 *   const foo = [1,2,3,4,5,6,7,8,9,10]
 *   foo.chunk(3)
 *   [[1,2,3], [4,5,6], [7,8,9], [10]
 */
Object.defineProperty(Array.prototype, 'chunk', {
  value: function(n) {
    return Array.from(Array(Math.ceil(this.length / n)), (_, i) =>
      this.slice(i * n, i * n + n)
    );
  }
});


/**
 * Date.getWeekNumber() - returns int of current week of the year
 */
Date.prototype.getWeekNumber = function() {
  var d = new Date(
    Date.UTC(this.getFullYear(), this.getMonth(), this.getDate())
  );
  var dayNum = d.getUTCDay() || 7;
  d.setUTCDate(d.getUTCDate() + 4 - dayNum);
  var yearStart = new Date(Date.UTC(d.getUTCFullYear(), 0, 1));
  return Math.ceil(((d - yearStart) / 86400000 + 1) / 7);
};