javascript es6 shallow array flatten for 2,3...n levels

es6-shallow-flatten.js

const deep2array = [
  ['abc1', 'bcd1', 'def1'], 
  ['abc2', 'bcd2', 'def2'], 
  ['abc3', 'bcd3', 'def3']
];

const shallowFlatten = (p, c) => [...p, ...c];
console.log(deep2array.reduce(shallowFlatten, []))
/* output:
["abc1", "bcd1", "def1", "abc2", "bcd2", "def2", "abc3", "bcd3", "def3"]
*/

const deep3array = [
  [
    ['abc11', 'bcd11', 'def11'],
    ['abc12', 'bcd12', 'def12'],
  ],
  [
    ['abc21', 'bcd21', 'def21'],
    ['abc22', 'bcd22', 'def22'],
  ], 
  [
    ['abc31', 'bcd31', 'def31'],
    ['abc32', 'bcd32', 'def32'],
  ]
];

console.log(deep3array.reduce(shallowFlatten, []).reduce(shallowFlatten, []))

/* output:
["abc11", "bcd11", "def11", "abc12", "bcd12", "def12", "abc21", "bcd21", "def21", "abc22", "bcd22", "def22", "abc31", "bcd31", "def31", "abc32", "bcd32", "def32"]
*/

// inline
console.log(deep2array.reduce((p, c) => [...p, ...c], []))