Remove the object of a specific index in a JSON array without leaving "null" behind (Node.js)

Question

I have a local JSON file under the path static/json/test.json. Its content is [{"id": 12}, {"id": 44}]. I want to read it, delete the object of the index i from it and rewrite the file so if for example i = 0 the new content should be [{"id": 44}].

What i have tried so far:

let i = 0;

fs.readFile("static/json/test.json", "utf8", function(err, data) {
    let obj = JSON.parse(data); // obj is now [{"id": 12}, {"id": 44}]
    delete obj[i];
    fs.writeFile("static/json/test.json", JSON.stringify(obj), "utf8");
    // test.json should now be [{"id": 44}], but its [null, {"id": 44}]
});

If I do this, the content of test.json isn't [{"id": 44}], it's [null, {"id": 44}].

I've read about using obj.splice(i, 1); instead of delete obj[i];, but for some reason that doesnt do anything, without me recieving any errors.

How do I remove the object of index i of this JSON array without leaving null behind?

Edit:

Thanks for the fast answers! Typically obj.splice(i, 1); should work, the cause why it doesn't for me has to have to do with my setup. The working answer for me is

let i = 0;

fs.readFile("static/json/test.json", "utf8", function(err, data) {
    let obj = JSON.parse(data); // obj is now [{"id": 12}, {"id": 44}]

    delete obj[i];
    obj = obj.filter(item => item);

    fs.writeFile("static/json/test.json", JSON.stringify(obj), "utf8");
    // test.json is now [{"id": 44}]
});

Using the code you show here with obj.splice(i, 1) instead of delete obj[i] works perfectly fine and results in test.json to be [{"id":44}]. There must be an other problem with your setup that should be fixed instead of looking for a workaround. What is the console output when you write obj.splice(i, 1); console.dir(JSON.stringify(obj)); instead of delete obj[i] — t.niese
– t.niese, Commented Oct 27, 2018 at 15:45

A l w a y s S u n n y · Accepted Answer · 2018-10-27 15:51:25Z

2

You can do delete and filter out undefined

const obj= [{"id": 12}, {"id": 44}]
delete obj[0];
console.log(obj.filter(item => item));

BUT splice() works OK

const obj= [{"id": 12}, {"id": 44}]
obj.splice(0, 1);
console.log(obj);

edited Oct 27, 2018 at 15:51

answered Oct 27, 2018 at 15:38

A l w a y s S u n n y

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2 Comments

Jared Smith Over a year ago

If you're filtering, why bother with delete?

A l w a y s S u n n y Over a year ago

Yes I agree, only filter will do the trick. But as OP used already delete, So I just do the undefined filter

Terry Lennox · Accepted Answer · 2018-10-27 16:05:32Z

0

You can use Array.splice to do this

// The item index to remove
let index = 0;
let arr = [{id: 12}, {id: 44}];
arr.splice(index,1);
console.log("Array after removing item", arr);

edited Oct 27, 2018 at 16:05

answered Oct 27, 2018 at 15:53

Terry Lennox

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