javascript - 当该成员从数组中删除时，我们如何访问该成员？

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var arr = [{id: 1, name: 'John'}, {id: 2, name: 'Mike'}];

var member = arr[0];

arr.splice(0, 1);

console.log(member);

Answer 1

您可以继续访问它，因为您仍然拥有对它的引用。它不再存在于数组中，但仍然存在。它将继续存在，直到对它的所有引用都被删除，当它们被删除时，它就符合垃圾回收的条件。

在此之后:

var arr = [{id: 1, name: 'John'}, {id: 2, name: 'Mike'}];

你的内存中有这样的东西(省略了一些细节):

                  +−−−−−−−−−−−−+arr:Ref4875−−−−−−>|   (array)  |                  +−−−−−−−−−−−−+      +−−−−−−−−−−−−−−+                  | 0: Ref8612 |−−−−−>|   (object)   |                  | 1: Ref4631 |−−+   +−−−−−−−−−−−−−−+                  +−−−−−−−−−−−−+  |   | id: 1        |                                  |   | name: "John" |                                  |   +−−−−−−−−−−−−−−+                                  |                                  |   +−−−−−−−−−−−−−−+                                  +−−>|   (object)   |                                      +−−−−−−−−−−−−−−+                                      | id: 1        |                                      | name: "John" |                                      +−−−−−−−−−−−−−−+

(The "Ref1234" values are called object references. You never see their actual values, but you can think of them as a number the JavaScript engine uses to look up where the object is in memory.)

Then after this:

var member = arr[0];

member 和数组都引用该对象，如下所示:

member:Ref8612−−−−−−−−−−−−−−−−−−−−−+                  +−−−−−−−−−−−−+   |arr:Ref4875−−−−−−>|   (array)  |   |                  +−−−−−−−−−−−−+   |  +−−−−−−−−−−−−−−+                  | 0: Ref8612 |−−−+−>|   (object)   |                  | 1: Ref4631 |−−+   +−−−−−−−−−−−−−−+                  +−−−−−−−−−−−−+  |   | id: 1        |                                  |   | name: "John" |                                  |   +−−−−−−−−−−−−−−+                                  |                                  |   +−−−−−−−−−−−−−−+                                  +−−>|   (object)   |                                      +−−−−−−−−−−−−−−+                                      | id: 1        |                                      | name: "John" |                                      +−−−−−−−−−−−−−−+

Then after:

arr.splice(0, 1);

数组不再有对它的引用，但 member 仍然有:

                                      +−−−−−−−−−−−−−−+member:Ref8612−−−−−−−−−−−−−−−−−−−−−−−>|   (object)   |                  +−−−−−−−−−−−−+      +−−−−−−−−−−−−−−+arr:Ref4875−−−−−−>|   (array)  |      | id: 1        |                  +−−−−−−−−−−−−+      | name: "John" |                  | 0: Ref4631 |−−+   +−−−−−−−−−−−−−−+                  +−−−−−−−−−−−−+  |                                   |                                   |                                   |                                   |                                  |   +−−−−−−−−−−−−−−+                                  +−−>|   (object)   |                                      +−−−−−−−−−−−−−−+                                      | id: 1        |                                      | name: "John" |                                      +−−−−−−−−−−−−−−+