无法获得正确的数组长度

Question

The code below returns the length of an array

var test=[];
test["abc"]=1;
test["abcd"]=11;
console.log(test.length);

I expected it outputs 2 but it displays 0

Your comment welcome

Answer 1

You aren't actually adding any elements to the array, this is creating properties on the array object.

You can tell that I am saying the truth by typing this:

console.log(test.abc);
console.log(test.abcd);

The length would have been increased probably if you had added the elements using push() or set them using a numerical index like:

test[0] = 1;
test[1] = 2;

Answer 2

You should count the number of keys using Object.keys :

console.log(Object.keys(test).length); // 2

Ideally, don't use array but a plain JavaScript object (also called hash ):

var test = {};
test.abc = 1;
test.abcd = 11;

Answer 3

Your problem is due to a misunderstanding of what consitutes and array in Javascript.

In Javascript, an array is specified as a specific type of object, consisting of only numeric keys.

The .length is a special property of the array object, which is tied to the value of the largest numeric key in the array.

By using keys such as "abc" , you are in fact merely setting arbitrary properties on the object; the length property will be completely unaffected by this.

You have two options:

1. Use numeric keys for your array.

2. If you need to use named keys, you will have to accept that the length property and other array-specific features are not available. So you may as well use a regular object rather than an array.

   It is still possible to count the elements in an object, but it's not as simple as just using a length property.

Answer 4

If you want to add items to the array use

 array[0] = 1;
 array[1] = 11;

Otherwise you are adding properties to the array