The Array Map method in JavaScript transforms each element within the array

Question

The Array Map method in JavaScript transforms each element within the array

I have a vector of objects in JavaScript (React Native) and I am trying to assign a unique random key to each item in the array. However, when I add the key property to one object, it ends up being the same for every element in the array.

It's puzzling me as to why this issue is occurring.

The original array looks like this:

[{"nome":"insalata di mare","prezzo":0.3,"qr_code":"qr_valore","quantita":3},{"nome":"insalata di mare","prezzo":0.3,"qr_code":"qr_valore","quantita":3}]

The resulting array is as follows:

Random product list: [{"nome":"insalata di mare","prezzo":0.3,"qr_code":"qr_valore","quantita":3,"key":"x4idec"},{"nome":"insalata di mare","prezzo":0.3,"qr_code":"qr_valore","quantita":3,"key":"x4idec"}]

This issue seems to occur only when the items are identical.

componentWillMount(){

    this.props.productList.map(item => {
      item.key = Math.random().toString(36).substring(7)
    })

}

The desired outcome should be a different key assigned to each object, something like this:

Random product list: [{"nome":"insalata di mare","prezzo":0.3,"qr_code":"qr_valore","quantita":3,"key":"x4idec"},{"nome":"insalata di mare","prezzo":0.3,"qr_code":"qr_valore","quantita":3,"key":"d2jdss"}]

javascript arrays react-native dictionary

Answer 1

Answer №1

Have you confirmed that each item in the array is actually a unique object?

Consider this scenario:

let a = {foo: 'bar'};
let b = a;
let array = [a, b];

In this case, the array will contain:

[{foo: 'bar'}, {foo: 'bar'}]

If you use the map method as demonstrated above, both items will change simultaneously because they are referencing the same object. This means that the changes affect all instances of that object within the array.

array.map((item, index) => item.key = index)

Will output:

[{foo: 'bar', key: 1}, {foo: 'bar', key: 1}]

Rather than

[{foo: 'bar', key: 0}, {foo: 'bar', key: 1}]

, which may have been your intended result.

To ensure that each element in the array can be modified independently, it is essential to guarantee that each item is a distinct object. Utilizing tools like lodash's clone function can aid in achieving this.

array.map((item, index) => _.clone(item).key = index)

Answer 2

Have you confirmed that each item in the array is actually a unique object?

Consider this scenario:

let a = {foo: 'bar'};
let b = a;
let array = [a, b];

In this case, the array will contain:

[{foo: 'bar'}, {foo: 'bar'}]

If you use the map method as demonstrated above, both items will change simultaneously because they are referencing the same object. This means that the changes affect all instances of that object within the array.

array.map((item, index) => item.key = index)

Will output:

[{foo: 'bar', key: 1}, {foo: 'bar', key: 1}]

Rather than

[{foo: 'bar', key: 0}, {foo: 'bar', key: 1}]

, which may have been your intended result.

To ensure that each element in the array can be modified independently, it is essential to guarantee that each item is a distinct object. Utilizing tools like lodash's clone function can aid in achieving this.

array.map((item, index) => _.clone(item).key = index)

Answer 3

Answer №2

Expanding on the points made by @kshetline.

I am of the opinion that this solution meets your requirements without relying on an external library.

const updatedProducts = this.props.productsList.map((product, index) => ({
  ...product,
  key: index
}));

One important thing to note is that a new object will be generated in this process, potentially overwriting any existing 'key' property!

Please share your thoughts on this approach!

Answer 4

Expanding on the points made by @kshetline.

I am of the opinion that this solution meets your requirements without relying on an external library.

const updatedProducts = this.props.productsList.map((product, index) => ({
  ...product,
  key: index
}));

One important thing to note is that a new object will be generated in this process, potentially overwriting any existing 'key' property!

Please share your thoughts on this approach!

The Array Map method in JavaScript transforms each element within the array

Answer №1

Answer №2

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