array-utils.js

/**
 * Moves to the end all "falsy" items within the array (this).
 *
 * Could be used for extending Array.prototype:
 * Array.prototype.separate = separate;
 *
 * @param [test] {Function} - function to determine whether an item is falsy
 *      if not provided, "falsy" is Boolean(value) except zero.
 * @returns {number} - first "falsy" item index
 */
export function separate(test) {
    test = typeof test === 'function' ? test : value => Boolean(value) || value === 0;
    let i = 0;
    let last  = 0;
    const {length} = this;
    while (i < length) {
        if (!test(this[i])) {
            i++;
            continue;
        }

        let j = i;
        while (j > last) {
            [this[j], this[j - 1]] = [this[j - 1], this[j]];
            j--;
        }

        i++;
        last++;
    }

    return last;
}

/**
 * Moves to the end all "falsy" items within the passed array.
 *
 * @param array
 * @param [test] {Function} - function to determine whether an item is falsy
 *      if not provided, "falsy" is Boolean(value) except zero.
 * @returns {number} - first "falsy" item index
 */
export function separate_array(array, test) {
    return separate.call(array, test);
}