One JS small knowledge point every day Javascript multi-dimensional array flattening

One JS small knowledge point every day Javascript multi-dimensional array flattening

var myArray = [[1, 2],[3, 4, 5], [6, 7, 8, 9]];
Request to return: [1, 2, 3, 4, 5, 6, 7, 8, 9 ]

1. Use concat() and apply()

var myNewArray = [].concat.apply([], myArray);
// [1, 2, 3, 4, 5, 6, 7, 8, 9]

2. Use reduce()

var myNewArray = myArray.reduce(function(prev, curr) {
    
    
  return prev.concat(curr);
});
// [1, 2, 3, 4, 5, 6, 7, 8, 9]

3. for loop

var myNewArray3 = [];
for (var i = 0; i < myArray.length; ++i) {
    
    
  for (var j = 0; j < myArray[i].length; ++j)
    myNewArray3.push(myArray[i][j]);
}
console.log(myNewArray3);
// [1, 2, 3, 4, 5, 6, 7, 8, 9]

4. Use ES6's spread operator

var myNewArray4 = [].concat(...myArray);
console.log(myNewArray4);
// [1, 2, 3, 4, 5, 6, 7, 8, 9]

5. Use Lodash's flattenDeep()

_.flattenDeep([1, [2, [3, [4]], 5]]);
// => [1, 2, 3, 4, 5]