How can I push the modified static field data in the array returned by the function after each change of the static field?

Question

Here is an example. I have class WalmartCart and I can't change it.

class WalmartCart {
    static cart = []
    putItem(item){
        WalmartCart.cart.push(item)
    }
}

And I need to have a function func which accepts the class as input and returns the array with modified items in static cart in WalmartCart.

const func = (WalmartCart) => {}

So, the result should look like this

let result = func(WalmartCart) // !!
let wal = new WalmartCart()

wal.putItem( {'1': 1} )
wal.putItem( {'2': 2} )
wal.putItem( {'3': '3'} )

console.log(result) 

// result =  [
//    {'1': 1, 'some new data': 'new data'}, 
//    {'2': 2, 'some new data': 'new data'}, 
//    {'3': '3', 'some new data': 'new data'}
// ]

The whole catch is that the function func can be called only once before putting the items in the static cart.

So, how can I do that?

just `return Walmart.cart`, it will assign a reference to the array to `result` which will reflect all changes made to the other references to the same array. see: [Is JavaScript a pass-by-reference or pass-by-value language?](https://stackoverflow.com/questions/518000/is-javascript-a-pass-by-reference-or-pass-by-value-language) and read the documentation [Array](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array) — pilchard, Sep 12 '22 at 04:49

Nick Vu · Answer 1 · 2022-09-12T05:44:08.023

You can return WalmartCart.cart directly in func

Like many other programming languages, Javascript also has call-by-sharing which is using a reference as a medium to the actual values.

class WalmartCart {
    static cart = [] //reference value
    putItem(item){
        WalmartCart.cart.push(item)
    }
}

const func = (WalmartCart) => {
  return WalmartCart.cart
}

let result = func(WalmartCart) //now `result` and `WalmartCart.cart` have the same reference value

console.log(`Is result and WalmartCart.cart is the same reference value: ${result === WalmartCart.cart}`)

let wal = new WalmartCart()

//`WalmartCart.cart` modification means `result` modification as well
wal.putItem( {'1': 1} ) 
wal.putItem( {'2': 2} )
wal.putItem( {'3': '3'} )

console.log(result)

some explanation about referencing would greatly improve this answer — pilchard, Sep 12 '22 at 04:53

score 0 · Answer 2 · answered Sep 12 '22 at 04:51

Just const func = (T) => T.cart

live demo:

const func = (T) => T.cart

class WalmartCart {
    static cart = []
    putItem(item){
        WalmartCart.cart.push(item)
    }
}

let result = func(WalmartCart)
let wal = new WalmartCart()
wal.putItem( {'1': 1} )
wal.putItem( {'2': 2} )
wal.putItem( {'3': '3'} )

console.log(result)

.as-console-wrapper { max-height: 100% !important; top: 0 }

How can I push the modified static field data in the array returned by the function after each change of the static field?

2 Answers2