Referencing Object within Object Javascript Confusion

Question

I am trying to create a reference to an object within an object, rather than creating a copy of it. I'm confused about reference vs. copy. What confuses me:

let master = {}
master['SomeObject'] = {a:"Something",b:"something"}
let subMaster = master['SomeObject']
subMaster['Test'] = true
console.log(master['SomeObject']['Test'])
//this WORKS as expected updating the original object
delete master['SomeObject']
console.log(subMaster)
//still shows content, and can continue to be manipulated? Shouldnt it show undefined?

Why does the reference still work even after deleting the original object? If I'm misunderstanding references, how can I make sure the original object is deleted so all references no longer work? I'm probably missing something fundamental and I appreciate anyones help!

maraaaaaaaa · Accepted Answer · 2022-01-28 20:22:54Z

2

delete does not physically delete the object from memory. It only removes that property from master. Since you are still referencing the object from your variable, and your variable has not fallen out of scope, the object still resides in memory.

Per MDN:

The JavaScript delete operator removes a property from an object

answered Jan 28, 2022 at 20:22

maraaaaaaaa

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6 Comments

sychordCoder Over a year ago

thank you, so if I were to add subMaster = undefined would that allow the original object to be removed from memory?

sychordCoder Over a year ago

also, if its based on all existing references, what if an object has a method that uses the 'this' reference to access internal properties? Would that prevent the object from being removed from memory?

maraaaaaaaa Over a year ago

@sychordCoder for your first question, no it would not. All referencing variables/properties must fall out of scope or be set to undefined. If you set EVERY reference to that object to undefined or null or some other object, only then it will be removed from memory.

maraaaaaaaa Over a year ago

@sychordCoder I'm not exactly sure what your asking in the second question

sychordCoder Over a year ago

is there a programmatic way to remove all references to an object or do I need to just go through and set them all to null? For the second part, if an object has a method let obj = {a:something,method(){return this.a}} would the 'this' reference within the method prevent it from being removed?

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