static count(arr, value) {
    let count = 0;

    for (let i = 0; i < arr.length; i++) {
      if (arr[i] === value) {
        count++;
      }
    }

    return count;
  }
Count the number of occurences of a value in an array.

@static
@param {Array} arr An array.
@param {*} value A value to be counted.
@returns {Number} The number of occurences of a value in the array.