Flatten nested JavaScript object

Question

I have a nested object and I want to flatten/map it into a single-layered, table-like object.

[{
    a: 1,
    b: 2,
    c: [{
        x: 10,
        y: 20
    }, {
        x: 30,
        y: 40
    }]
}, {
    a: 3,
    b: 4,
    c: [{
        x: 50,
        y: 60
    }, {
        x: 70,
        y: 80
    }]
}]

From that, I want to get something like this:

[{
    a: 1,
    b: 2,
    x: 10,
    y: 20
}, {
    a: 1,
    b: 2,
    x: 30,
    y: 40
}, {
    a: 3,
    b: 4,
    x: 50,
    y: 60
}, {
    a: 3,
    b: 4,
    x: 70,
    y: 80
}]

Sure, I could simply iterate over the object with two for loops and put the result info a separate array, but I wonder, if there is a simpler solution. I already tried to play around with flatMap. It works, if I only want the c portion of my nested object, but I don't know how to map a and b to this object.

As some of you asked for some working code, this should do it (untested):

let result = [];

for (const outer of myObj)
  for (const inner of outer.c)
    result.push({a: outer.a, b: outer.b, x: inner.x, y: inner.y});

The question is, if there is a functional one-liner or even another, better approach. In reality, my object consists of four layers and the nested for loops become messy quite fast.

Answer 1

You may use flatMap method alongwith map on property 'c':

var input = [{ a: 1, b: 2, c: [{ x: 10, y: 20 }, { x: 30, y: 40 }] }, { a: 3, b: 4, c: [{ x: 50, y: 60 }, { x: 70, y: 80 }] }];

const output = input.flatMap(obj =>
  obj.c.map(arr => ({a: obj.a, b: obj.b, x: arr.x, y: arr.y}))
);

console.log(output);