Flatten a multi dimensional array to 1D array

flatten-array.js

'use strict';

/**
 * @method flattenArray
 * @description A method to convert multi dimensional arrays to 1D arrays
 * @param {Array} arr - The multi D array that needs to be flattened (converted to 1D)
 * @param {String} [key] - An object key that will be used to flatten an array of
 * nested objects (e.g. "[ { key: [ val1, val2, ..., valN ] }, { key: [ val1, val2, ..., valN ] } ]")
 * @param {Boolean} [remove] - Flag to indicate whether or not to delete object's children if
 * they are not need it after flattening (e.g. if true, will remove "key: [ val1, val2, ..., valN ]" after it is being flattened)
 * @return {Array} Flattened array
 */
function flattenArray(arr, key, remove) {
    if (!Array.isArray(arr)) {
        console.warn(`${new Date()}: the passed argument is not an array:`, arr);

        return arr;
    }

    const result = arr.reduce((prev, curr) => {
        const isObject = !!curr[key];
        const nestedItem = isObject ? curr[key] : curr;
        const isArray = Array.isArray(nestedItem);
        let finalArr = (isObject || !isArray) ? prev.concat(curr) : [];

        if (isArray) {
            if (isObject) {
                finalArr = finalArr.concat(flattenArray(nestedItem, key, remove));

                if (remove) {
                    delete curr[key];
                }
            } else {
                // pass the key in case a deeper nested object needs to be flattened
                finalArr = prev.concat(flattenArray(nestedItem, key, remove));
            }
        }

        return finalArr;
    }, []);

    return result;
}