可变数组在js中如何工作？

Question

i'm Learning Javascript from multiple ressources like FCC where i can't Understand one concept with the mutable arrays. I've got an example :

var myArray = [1,2,3];
myArray[0]=3;  //[3,2,3]

var ourArray = [1,2,3];
ourArray[1] = 3; //[1,3,3]

i can't get how the [3,2,3] and [1,3,3] are created.

thanks for your help

ok, got it but what if my code looks like this :

var arr = [ [1,2,3], [4,5,6], [7,8,9], [[10,11,12], 13, 14] ];
arr[3];  // equals [[10,11,12], 13, 14] arr[3][0]; // equals [10,11,12]
arr[3][0][1]; // equals 11 how the arr[3] or arr[3][0] work ?

Answer 1

Arrays in JS starts with 0 index.
In the first case you're replacing 1 with 3

[1, 2, 3]
 ^
 3
[0, 1, 2] <- indexes

In the second case, you're replacing 2 with 3

[1, 2, 3]
    ^
    3
[0, 1, 2] <- indexes

Answer 2

Mutable just means that each element in the array can be changed. The number inside the brackets is the order starting with 0;

So originally myArray[0] is 1, myArray[1] is 2, myArray[2] is 3 When you do myArray[0] = 3 it sets the value in the first spot to 3, hence getting 3,2,3

Answer 3

当您在此处写入myArray[0]=3 ，您要在该数组中设置一个与ourArray[1]相同的特定位置的值，以便在该数组中使用新值进行更改，以便控制台为您提供具有新值的数组就像在您的示例中一样，您使用名称myArray和ourArray进行了定义。

Answer 4

Let me go through your code line by line,

var myArray = [1,2,3];

creates a myArray with [1, 2, 3]

myArray[0]=3;

index 0 of myArray is set to 3;

so myarray holds [3, 2, 3]

var ourArray = [1,2,3];

ourArray is created with [1, 2, 3]

ourArray[1] = 3;

index 1 of our array is set to 3; so our array holds [1, 3, 3]

Please note that index starts with 0 and not with 1.