javascript - array reference is not cleared

Question

When I assign anotherArrayList = arrayList, anotherArrayList is a pointer to arrayList. So why this does not work when I empty the arrayList.

var arrayList = ['a', 'b', 'c', 'd', 'e', 'f']; 
var anotherArrayList = arrayList;  

arrayList[1] = '15';

console.log(arrayList); // output: [ "a", "15", "c", "d", "e", "f" ]
console.log(anotherArrayList); // output: [ "a", "15", "c", "d", "e", "f" ]

arrayList = []; 
console.log(arrayList); // output: []
console.log(anotherArrayList); // output: [ "a", "15", "c", "d", "e", "f" ]

When you do arrayList = []; you aren't changing the object that arrayList was pointing at; you're making arrayList point at a new object. Your premise is wrong: "I empty the arrayList" is not what's happening. — user5734311
– user5734311, Commented Feb 20, 2019 at 12:14
Possible duplicate of Is it possible to have 2 variables pointing to the same object? (javascript) — adiga
– adiga, Commented Feb 20, 2019 at 12:21
Possible duplicate of Are there pointers in javascript? and js replace object / change reference — adiga
– adiga, Commented Feb 20, 2019 at 12:27
Does this answer your question? Pass-by-reference JavaScript objects — Ivar
– Ivar, Commented Jun 10, 2020 at 20:52

Nina Scholz · Accepted Answer · 2019-02-20 12:18:31Z

2

By assigning a new array, the old object reference gets a new reference to the empty array.

You could assign zero to the length property which empties the object reference as well.

var arrayList = ['a', 'b', 'c', 'd', 'e', 'f'],
    anotherArrayList = arrayList;

arrayList[1] = '15';

console.log(arrayList);        // [ "a", "15", "c", "d", "e", "f" ]
console.log(anotherArrayList); // [ "a", "15", "c", "d", "e", "f" ]

arrayList.length = 0; 
console.log(arrayList);        // []
console.log(anotherArrayList); // []

edited Feb 20, 2019 at 12:18

answered Feb 20, 2019 at 12:15

Nina Scholz

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1 Comment

NemoStein Over a year ago

This doesn't answer he question.

Nick Parsons · Accepted Answer · 2019-02-20 12:17:57Z

2

It doesn't empty your other array because you're not actually clearing/emptying it, instead you are creating a new empty array in memory, which arrayList will point to, whereas anotherArrayList will still point to the full array.

Instead, to empty the array itself, you can use the .length property: arrayList.length = 0

var arrayList = ['a', 'b', 'c', 'd', 'e', 'f']; 
var anotherArrayList = arrayList;  

arrayList[1] = '15';

console.log(arrayList); // output: [ "a", "15", "c", "d", "e", "f" ]
console.log(anotherArrayList); // output: [ "a", "15", "c", "d", "e", "f" ]

arrayList.length = 0; 
console.log(arrayList); // output: []
console.log(anotherArrayList); // output: []

answered Feb 20, 2019 at 12:17

Nick Parsons

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Comments

Shashank · Accepted Answer · 2019-02-20 12:20:49Z

0

Array and objects are non-primitive data-type in javascript. When a variable is assigned with reference to a non-primitive data-type, the copy of memory location is stored in that new variable.

answered Feb 20, 2019 at 12:20

Shashank

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