JS如何展平嵌套数组

Question

The question I have been given is;

Given a nested array or arrays, return a new, flat array with all the elements of all the nested arrays in their original order

The answer that I have come up with is;

function flattenArray (arrayOfArrays) {  
arrays = arrays.reduce(function(a, b){
    return a.concat(b);
}, []);

console.log(merged);

My answer is being tested against this;

describe("flattenArray", () => {
it("returns a flat array with all the elements of the nested arrays in      their original order", () => {
  let arrayOfArrays, expected;
  arrayOfArrays = [[1, 2], [], [3], ["hello", true]];
  expected = [1, 2, 3, "hello", true];
  expect(flattenArray(arrayOfArrays)).to.eql(expected);

  arrayOfArrays = [[1], [2], [[3, 4]]];
  expected = [1, 2, [3, 4]];
  expect(flattenArray(arrayOfArrays)).to.eql(expected);
});
it("does not mutate the passed array, i.e. returns a new array, leaving the original untouched", () => {
  const original = [[1, 2], [], [3, 4]];
  const flat = flattenArray(original);
  expect(original).to.not.equal(flat);
  expect(original).to.eql([[1, 2], [], [3, 4]]);
});
});

I have no clue how else to try and solve this question, does anyone have any sugestions.

Answer 1

You need to return the reduced array by taking the handed over array arrayOfArrays .

function flattenArray(arrayOfArrays) {  
    return arrayOfArrays.reduce(function(a, b) {
        return a.concat(b);
    }, []);
}

For multiple nested arrays, you need to check for array and use a recursion of the function.

 function deepFlattenArray(arrayOfArrays) { return arrayOfArrays.reduce(function(a, b) { return a.concat(Array.isArray(b) ? deepFlattenArray(b) : b); }, []); } function flattenArray(arrayOfArrays) { return arrayOfArrays.reduce(function(a, b) { return a.concat(b); }, []); } console.log(deepFlattenArray([[[1, 2], [3, [4, 5], 6], 7], 8])); console.log(flattenArray([[[1, 2], [3, [4, 5], 6], 7], 8])); 

 .as-console-wrapper { max-height: 100% !important; top: 0; } 

Answer 2

Perhaps not the most elegant solution, but this will flatten any number of nested arrays. It's a recursive function that modifies a new array as a side-effect:

 var arrOfArrs = [[1, 2, 3], [4, 5, 6], 7, [8, [9, 10, 11, 12]]]; newArr = []; function flattenArray(arr) { for(var i=0; i < arr.length; i++) { typeof arr[i] == 'object' ? flattenArray(arr[i]) : newArr.push(arr[i]); } } flattenArray(arrOfArrs); console.log(newArr); 

Answer 3

You can use reduce plus spread operator. Just coded this for the particular question but seems to work ok. It uses recursion and works for Multiple nested arrays.

 function flatArray(a){ return a.reduce( (accumulator, current) => { if (!Array.isArray(current)) return [...accumulator, current]; return flatArray([...accumulator, ...current]); }, []); } let a = [ 1, [2], [3,4], [], [5], [6, [7]], [[[8]]] ]; console.log(flatArray(a));