Copy specific array elements to an existing object (overwrite)

Question

I have the following objects

var obj1 = 
[
    {
        "id": 1373744172,
        "name": "Run",
        "distance": 6051.8,
        "date": "2018-01-24T16:43:09Z",
    },
    {
        "id": 1370355715,
        "name": "Swim",
        "distance": 1043,
        "date": "2018-01-22T21:10:28Z",
    }
]

var dest = 
[
    {title: "Placeholder", body: "1900-01-01T00:00:00Z"}
]

I am trying to overwrite the dest based on obj1, so I should end up with

[
    {title: "Run", body: "2018-01-24T16:43:09Z"},
    {title: "Swim", body: "2018-01-22T21:10:28Z"}
]

I've looked at Object.assign, and for-in loops, but I've not yet figured out the right approach. e.g.

var obj1 = 
[
    {
        "id": 1373744172,
        "name": "Run",
        "distance": 6051.8,
        "date": "2018-01-24T16:43:09Z",
    },
    {
        "id": 1370355715,
        "name": "Swim",
        "distance": 1043,
        "date": "2018-01-22T21:10:28Z",
    }
]

var dest = 
[
    {title: "Placeholder", body: "1900-01-01T00:00:00Z"}
]

Object.assign(dest, {title: obj1.name, body: obj1.date});

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

I'm sure this must have been asked and answered before, but I don't seem to be searching with the right terms!

"e.g. jsfiddle.net/y9oL42wr" Put the code in the question, not just linked. Links rot, making the question (and somtimes its answers, probably not here) useless to people in the future, and people shouldn't have to go off-site to help you. Put a minimal reproducible example in the question, ideally using Stack Snippets (the <> toolbar button) to make it runnable (here's how to do one). More: How do I ask a good question? — T.J. Crowder
– T.J. Crowder, Commented Jan 26, 2018 at 11:09
Do you really want to change the array referenced by dest, or do you want a new array? (In the former case other references to the old array would see the updates; in the latter they wouldn't.) — Richard
– Richard, Commented Jan 26, 2018 at 11:09

Faly · Accepted Answer · 2018-01-26 11:09:10Z

5

You don't need Object.assign, use array.prototype.map to transform each element of your array:

var obj1 = 
[
    {
        "id": 1373744172,
        "name": "Run",
        "distance": 6051.8,
        "date": "2018-01-24T16:43:09Z",
    },
    {
        "id": 1370355715,
        "name": "Swim",
        "distance": 1043,
        "date": "2018-01-22T21:10:28Z",
    }
];

var dest = obj1.map(e => ({title: e.name , body: e.date}));

console.log(dest);

answered Jan 26, 2018 at 11:09

Faly

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Comments

Richard · Accepted Answer · 2018-01-26 14:56:15Z

0

To keep the same array instance (as clarified in the comments) Array.splice can be used, combined with Array.map to convert the new elements. But splice takes the new elements as additional parameters, so need to be a little clever about calling splice:

let args = [0, dest.length].concat(obj1.map(e=>({title: e.name, body: e.date})));
dest.splice.apply(dest, args);

answered Jan 26, 2018 at 14:56

Richard

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