how to map property with array of object inside in javascript

Question

I'm just trying to return my array completely using map, before I will start my next function. But I am receiving incomplete array when consoling it

This is my example array:

data = [{
        "a": 1,
        "b": 5,
        "c": 9,
        "d": 1,
        "e": 4,
        "f": 44,
        "g": 23,
        "h": 12,
        "i": 22,
        "j": 23,
        "k": [{
            "a": 1,
            "b": 5,
            "c": 9,
            "d": 1
        }, {
            "a": 1,
            "b": 5,
            "c": 9,
            "d": 1
        }]
    },
    {
        "a": 2,
        "b": 6,
        "c": 10,
        "d": 1,
        "e": 4,
        "f": 44,
        "g": 23,
        "h": 12,
        "i": 22,
        "j": 23,
        "k": [{
            "a": 1,
            "b": 5,
            "c": 9,
            "d": 1
        }, {
            "a": 1,
            "b": 5,
            "c": 9,
            "d": 1
        }]
    },
    {
        "a": 3,
        "b": 7,
        "c": 11,
        "d": 1,
        "e": 4,
        "f": 44,
        "g": 23,
        "h": 12,
        "i": 22,
        "j": 23,
        "k": [{
            "a": 1,
            "b": 5,
            "c": 9,
            "d": 1
        }, {
            "a": 1,
            "b": 5,
            "c": 9,
            "d": 1
        }]
    },
    {
        "a": 4,
        "b": 8,
        "c": 12,
        "d": 1,
        "e": 4,
        "f": 44,
        "g": 23,
        "h": 12,
        "i": 22,
        "j": 23,
        "k": [{
            "a": 1,
            "b": 5,
            "c": 9,
            "d": 1
        }, {
            "a": 1,
            "b": 5,
            "c": 9,
            "d": 1
        }]
    }
]

var result = data.map(x=>({...x}));     
console.log(result);

this is my array looks like when I am consoling it:

[{
        "a": 1,
        "b": 5,
        "c": 9,
        "d": 1,
        "e": 4,
        "f": 44,
        "g": 23,
        "h": 12,
        "i": 22,
        "j": 23,
        "k": []
    },
    {
        "a": 2,
        "b": 6,
        "c": 10,
        "d": 1,
        "e": 4,
        "f": 44,
        "g": 23,
        "h": 12,
        "i": 22,
        "j": 23,
        "k": []
    },
    {
        "a": 3,
        "b": 7,
        "c": 11,
        "d": 1,
        "e": 4,
        "f": 44,
        "g": 23,
        "h": 12,
        "i": 22,
        "j": 23,
        "k": []
    },
    {
        "a": 4,
        "b": 8,
        "c": 12,
        "d": 1,
        "e": 4,
        "f": 44,
        "g": 23,
        "h": 12,
        "i": 22,
        "j": 23,
        "k": []
    }
]

I want my array to be complete when I am using the .map() function.

Jack Bashford · Accepted Answer · 2019-06-13 09:32:31Z

3

Spreading is only a shallow copy - so the inner arrays won't be copied.

For a simple deep copy, use JSON.stringify and JSON.parse.

const data = [{"a":1,"b":5,"c":9,"d":1,"e":4,"f":44,"g":23,"h":12,"i":22,"j":23,"k":[{"a":1,"b":5,"c":9,"d":1},{"a":1,"b":5,"c":9,"d":1}]},{"a":2,"b":6,"c":10,"d":1,"e":4,"f":44,"g":23,"h":12,"i":22,"j":23,"k":[{"a":1,"b":5,"c":9,"d":1},{"a":1,"b":5,"c":9,"d":1}]},{"a":3,"b":7,"c":11,"d":1,"e":4,"f":44,"g":23,"h":12,"i":22,"j":23,"k":[{"a":1,"b":5,"c":9,"d":1},{"a":1,"b":5,"c":9,"d":1}]},{"a":4,"b":8,"c":12,"d":1,"e":4,"f":44,"g":23,"h":12,"i":22,"j":23,"k":[{"a":1,"b":5,"c":9,"d":1},{"a":1,"b":5,"c":9,"d":1}]}];

const res = data.map(x => JSON.parse(JSON.stringify(x)));
console.log(res);

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

There's also the less well-supported Object.fromEntries - this feature is currently in the draft stage:

const data = [{"a":1,"b":5,"c":9,"d":1,"e":4,"f":44,"g":23,"h":12,"i":22,"j":23,"k":[{"a":1,"b":5,"c":9,"d":1},{"a":1,"b":5,"c":9,"d":1}]},{"a":2,"b":6,"c":10,"d":1,"e":4,"f":44,"g":23,"h":12,"i":22,"j":23,"k":[{"a":1,"b":5,"c":9,"d":1},{"a":1,"b":5,"c":9,"d":1}]},{"a":3,"b":7,"c":11,"d":1,"e":4,"f":44,"g":23,"h":12,"i":22,"j":23,"k":[{"a":1,"b":5,"c":9,"d":1},{"a":1,"b":5,"c":9,"d":1}]},{"a":4,"b":8,"c":12,"d":1,"e":4,"f":44,"g":23,"h":12,"i":22,"j":23,"k":[{"a":1,"b":5,"c":9,"d":1},{"a":1,"b":5,"c":9,"d":1}]}];

const res = data.map(x => Object.fromEntries(Object.entries(x)));
console.log(res);

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

edited Jun 13, 2019 at 9:32

answered Jun 13, 2019 at 9:28

Jack Bashford

44.3k11 gold badges56 silver badges84 bronze badges

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4 Comments

Nina Scholz Over a year ago

that does not answer the question. if taking JSON, a complete stringify and parsing omits mapping.

Roberto Zvjerković Over a year ago

Recursive shallow copy will work faster and for objects that are not serializable. JSON.parse(JSON.stringify(x)) is never advised. You can use const clone = (items) => items.map(item => Array.isArray(item) ? clone(item) : item);

Jack Bashford Over a year ago

Ok @NinaScholz I'll add that to the answer

Jack Bashford Over a year ago

Thanks @ritaj, I'll add that to the answer

Victor · Accepted Answer · 2019-06-13 09:38:01Z

0

It is not because of map function it is because of console. The console can cut output if it is too long. If you need to see full result you can make

console.log(JSON.stringify(result));

Or some other code modifies nested arrays ( data[0].k = [] ). Since you are making high level copy you will see empty array. In this case you should make deep copy of the original data. For this case you there is a very useful lib lodash

So you can do this:

var result = _.cloneDeep(data);

answered Jun 13, 2019 at 9:38

Victor

4474 silver badges14 bronze badges

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