Assigned variable follows the changes of array unexpectedly

Question

I assign the new variable to an array. after modifying the array the assigned variable follows the changes of array unexpectedly!

let reference = "I was sent* to Earth,* to protect you."

let orders = reference.split("*").map(s => s.toLowerCase().replace(/\,|\?|\!|\:|\./g,'').trim());

let answer = orders;

console.log(orders)
console.log(answer)
// changing orders and not answer!
orders.push(orders.shift());

// the orders changes as expected but the answer (that is not changed before follows the orders changes)
console.log(orders)
console.log(answer)

kooskoos · Accepted Answer · 2020-01-09 12:07:18Z

2

let answer = orders;

You are copying reference of orders to answer as it is an array.

It's like giving another name to the same array(block of memory).

This should solve your problem

Change let answer = orders; to let answer = [...orders];

let reference = "I was sent* to Earth,* to protect you."

let orders = reference.split("*").map(s => s.toLowerCase().replace(/\,|\?|\!|\:|\./g,'').trim());

let answer = [...orders];

console.log(orders)
console.log(answer)
// changing orders and not answer!
orders.push(orders.shift());

// the orders changes as expected but the answer (that is not changed before follows the orders changes)
console.log(orders)
console.log(answer)

answered Jan 9, 2020 at 12:07

kooskoos

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4 Comments

user5607806 Over a year ago

What if I assign a variable to another variable (none of them is an array); like let var1 = var2

kooskoos Over a year ago

Then only the value is copied.

kooskoos Over a year ago

The variable that holds an array actually holds a reference to the memory location

kooskoos Over a year ago

If you were to do var a = arr[0] still only value is copied

coderman401 · Accepted Answer · 2020-01-09 12:22:06Z

1

let answer = orders.slice(0) will make a shallow copy of your array object. in my opinion, to copy your array object the solution is:

let answer = copy(orders);

// copy function
function copy(object) {
    var output, value, key;
    output = Array.isArray(object) ? [] : {};
    for (key in object) {
        value = object[key];
        output[key] = (typeof value === "object") ? copy(value) : value;
    }
    return output;
}

answered Jan 9, 2020 at 12:22

coderman401

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Comments

Andy Mardell · Accepted Answer · 2020-01-09 12:09:29Z

0

You're mutating the existing array. Clone it by doing the following:

let reference = "I was sent* to Earth,* to protect you."

let orders = reference.split("*").map(s => s.toLowerCase().replace(/\,|\?|\!|\:|\./g,'').trim());

let answer = [...orders];

console.log(orders)
console.log(answer)
// changing orders and not answer!
orders.push(orders.shift());

// the orders changes as expected but the answer (that is not changed before follows the orders changes)
console.log(orders)
console.log(answer)

Alternatively, you can use let answer = orders.slice(0) if you're not using es6

answered Jan 9, 2020 at 12:09

Andy Mardell

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Comments

uiTeam324 · Accepted Answer · 2020-01-09 12:10:18Z

0

This will solve your issue.

let answer = [...orders];

answered Jan 9, 2020 at 12:10

uiTeam324

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