Simple function for generating all possible configuration without repeating the items with possibility to specify the output length

generator_getAllPossibleCombinations.js

function* getAllPossibleCombinations(arr, outputLength = arr.length) {
  if (outputLength > arr.length) {
    throw 'Not enough items in array';
  }
  
  for (let i = 0; i < arr.length; i++) {
    if (outputLength === 1) yield arr[i];
    
    for (let j = 0; j < arr.length; j++) {
      if (i === j) continue;
      
      const r = arr[i] + arr[j];
      if (outputLength <= 2) yield r;
      
      const nextArr = arr.filter((_, index) => index !== i && index !== j);
      const iterator = getAllPossibleCombinations(nextArr, outputLength - 2);
      yield r + iterator.next().value;
    }
  }
};

getAllPossibleCombinations.js

function getAllPossibleCombinations(arr, outputLength = arr.length) {
  if (outputLength > arr.length) {
    console.warn('Not enough items in array');
    return [];
  }
  
  let output = [];
  for (let i = 0; i < arr.length; i++) {
    if (outputLength === 1) {
      output.push(arr[i]);
      continue;
    }
    
    for (let j = 0; j < arr.length; j++) {
      if (i === j) continue;
      
      const r = arr[i] + arr[j];
      if (outputLength <= 2) {
        output.push(r);
        continue;
      }
      
      const nextArr = arr.filter((_, index) => index !== i && index !== j);
      output.push(...getAllPossibleCombinations(nextArr, outputLength - 2).map(comb => r + comb));
    }
  }
  return output;
};

// Usage:
//   
//   generateAllPossibleCombinations(['a', 'b']);
//   output: ['ab', 'ba']
//
//   generateAllPossibleCombinations(['a', 'b', 'c'], 2);
//   output: ['ab', 'ac', 'ba', 'bc', 'ca', 'cb']
//