flattened.js

/**
 * Write some code, that will flatten an array of arbitrarily nested arrays of integers into a 
 * flat array of integers. e.g. [[1,2,[3]],4] -> [1,2,3,4]. 
 **/

/**
* forEach solution
**/
const FlatLinerFE = function(arr) {
	let flatline = [];
	let flattFE = function(set) { 
		set.forEach( currVal => Array.isArray(currVal) ? flattFE(currVal) : flatline.push(currVal) );
	};

	// check if arr is array if not bail out early
  	Array.isArray(arr) ? flattFE(arr) : flatline = arr;

	return flatline;
	
};

/**
 * Map solution
 **/
const FlatLinerMap = function(arr) {
	let flatline = [];
  	let flattMap = (set) => { 
      set.map((a,v,c) => { 
          Array.isArray(a) ? flattMap(a) : flatline.push(a); 
      });
  	};
	// check if arr is array if not bail out early
  	Array.isArray(arr) ? flattMap(arr) : flatline = arr;

	return flatline;
};

/**
 * Reduce recursive solution
 **/
const FlatLinerReduceRecursive = function(arr) {
  let flattReduce = set => set.reduce ((newArr, currVal ) => {
	return newArr.concat(Array.isArray(currVal) ? flattReduce(currVal) : currVal), []);
  }
  // check if arr is array if not bail out early
  return Array.isArray(arr) ? flattReduce(arr) : arr;
};

/**
 * Reduce non-recursive solution
 **/
const FlatLinerReduceStraight = function(arr) {
  let flattReduce = set => set.reduce ((newArr, currVal ) => {
	return newArr.concat(currVal), []);
  }
  // check if arr is array if not bail out early
  return Array.isArray(arr) ? flattReduce(arr) : arr;
};

/**
 * toString + reduce solution
 **/
const FlattenToString = function(A) {
	return A
	.toString()
	.split(',')
	.reduce( (a,c) => {
		let i = parseFloat(c);
		c = (!Number.isNaN(i)) ? i : c;
		a.push(c);
		return a;
	}, []);
};

/**
* JSON stringify solution
* thanks to: https://stackoverflow.com/users/2907495/r-santosh-reddy
* from this thread: https://stackoverflow.com/a/43541431/965703
**/
const FlattenJSON = function(A) {
	let B = JSON.parse(`[${JSON.stringify(A).replace(/\[|]/g,'')}]`);
	return B;
}

let single = "hello, paprika";
let arr = [1, [2, 3, [4, [5, [6] ] ] ] ];

console.group("Testing with array");
  	console.log("forEach:", FlatLinerFE(arr)); 
  	console.log("Map:", FlatLinerMap(arr));
 	console.log("Reduce Recursive:", FlatLinerReduceRecursive(arr));
	console.log("Reduce Straight:", FlatLinerReduceStraight(arr));
	console.log("Flatten toString + reduce:", FlattenToString(arr));
	console.log("Flatten JSON:", FlattenJSON(arr));
	
console.groupEnd();

console.group("Testing with non array");
  	console.log("forEach:", FlatLinerFE(single)); 
  	console.log("Map:", FlatLinerMap(single));
  	console.log("Reduce:", FlatLinerReduce(single));
	console.log("Reduce Recursive:", FlatLinerReduceRecursive(single));
	console.log("Reduce Straight:", FlatLinerReduceStraight(single));
	console.log("Flatten toString + reduce:", FlattenToString(single));
	console.log("Flatten JSON:", FlattenJSON(single));
console.groupEnd();