While testing out the following code:
const animals = ['pigs', 'goats', 'sheep'];
animals.push(animals)
console.log(animals);
An error occurred in my testing environment:
Issue: Maximum call stack size exceeded.
What is causing this code to create an endlessly nested array?
When you use the animals.push(animals) method, you are essentially pushing the array itself into the array. This results in a single array that keeps growing in size, with each new element being a reference to the original array. This leads to a nested structure like this:
['pigs', 'goats', 'sheep',
['pigs', 'goats', 'sheep',
['pigs', 'goats', 'sheep',
['pigs', 'goats', 'sheep',
...
]
]
]
]
Contrary to popular belief, this does not consume infinite memory, as it is all contained within one array. You can think of it as:
animals (ref)
│
│ ┌───────────────────────────────┐
v v │
┌──────────┬──────────┬──────────┬───│───────┐
│ "pigs" │ "goats" │ "sheep" │ (ref) │
└──────────┴──────────┴──────────┴───────────┘
If you wish to avoid this recursive behavior and just push ['pigs', 'goats', 'sheep'] without affecting the original array, you should create a new array with those values:
animals.push([...animals])
Now, your structure will look like this:
['pigs', 'goats', 'sheep', ['pigs', 'goats', 'sheep']]
Visualizing this arrangement:
animals (ref)
│
│
v
┌──────────┬──────────┬──────────┬───────────┐
│ "pigs" │ "goats" │ "sheep" │ (ref) │
└──────────┴──────────┴──────────┴───│───────┘
┌──────────────────────────────────┘
v
┌──────────┬──────────┬──────────┐
│ "pigs" │ "goats" │ "sheep" │
└──────────┴──────────┴──────────┘
As depicted, the nested array is now a separate array with 3 entries instead of 4.
This array may not be infinite in its nesting, but attempting to traverse it leads to an endless recursion.
animals = [ 'dog', 'cat' ];
animals.push(animals);
animals.push('zebra');
So when you try to
console.log(animals);
This is what happens (in pseudo-code):
for(each element in the array)
console.log(element);
element 0: dog
element 1: cat
element 2: an array - let's expand it!
To expand that array (which is the same array), it basically starts over:
element 0: dog
element 1: cat
element 2: an array - let's expand it!
And this cycle continues indefinitely. It never reaches the 'zebra' entry at any point.
Essentially, this is what happens when a recursive function keeps calling itself without any conditions:
function recur()
{
recur();
}
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