为什么array.push（）似乎无限次推？

Question

Consider the following javascript code,

>> a = [1, 2]
  Array [ 1, 2 ]

>> a.push(a) 
  Array [ 1, 2, Array[3] ] 

On expanding the array, a , we get an array with infinite depth. (as viewed on the firefox developer console)

Array[3]
| 0: 1
| 1: 2
  2: Array[3]
  | 0: 1
  | 1: 2
  | 2: Array[3]
    | 0: 1
    | 1: 2
    | 2: Array[3]
    ....

[1] Why is a getting appended more than once?
[2] At what depth does it stop?

Answer 1

It is just pushed once. While the array is referencing itself ( circular refernce ), you see more than one inserted arrays. The display is dependent of the browser.

If you try to get a JSON string, then JSON.stringify breaks with an error

 Circular reference in value argument not supported 

 var a = [1, 2] console.log(a); a.push(a); console.log(a); JSON.stringify(a); 

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

Answer 2

It's not getting pushed an infinite number of times. It's a matter of how Firefox Developer Console presents the element. Expanding the array and clicking on it again, under itself, will always show you how the array looks like. So you can expand it and click it an infinite number of times, but still, it's there only once .

Answer 3

You've created a circular reference.

When you push the array onto itself, the last element in the array becomes a reference to the entire array -- including that last element. So the last element in that last element is also a reference to the entire array, and so on.

It's infinite in the same sense that a circle is infinite, and "appends more than once" only in the same sense that if you go around a circle more than once you'll hit the same spot more than once.

Answer 4

Because the javascript gives the reference to the 'a' variable, and not the actual object, so if you push the a to itself, you push the memory address what hold the object, and it creates a circular reference.

[1, 2, reference to this object ]

Answer 5

It is actually pushing it only one time. It doesn't push the array elements, but the address of the array. Firefox console just tries to show what's in there, but ends up showing the same thing infinitely.

Not just Firefox, Chrome also does that.