CODEWITHSUNDEEP
javascriptarraysvue.js
374
374

Reputation: 129

Array/List length is zero but Array is not empty

When I console.log my array it shows that the length is zero. I checked that it was an array using Array.isArray which returned true. Also printed out the array values to make sure they exist and it shows in the console:

[]
0: "a"
1: "b"
2: "c"
3: "d"
length: 4
__proto__: Array(0)

I see that __proto__: Array(0) and I'm assuming this means it's a 0 length Array but how do I make it non-zero length so that I can iterate through it?

A thought I had is that this function might be asynchronous but I'm not really sure how to work around that.

Code for reference:

var list=[]
//getting data from a database
snapshot.forEach(function (node) {
   list.push(node.val())
   console.log(node.val()) //values print out
})
console.log(list) //array is length zero

I'm basically trying to add a for loop after this code to read through each value and use it for something else. However I can't iterate through the array because it registers as empty.

Upvotes: 8

Views: 26379

Answers (6)

猿助手
猿助手

Reputation: 1

Today I ran into this problem, if you use Vue2 or Vue3, maybe the field is not responsive, you can use Vue.set(target, key, value) or this.$set(target, key, value) to solve the problem!

Upvotes: 0

rTaylor
rTaylor

Reputation: 39

Similar problem and not a solution.

            printVertices(){ 
                console.log(Array.isArray(this.vertices), this.vertices)
                let head = "<head> "  
                            this.vertices = [] 
 
                console.log(this.vertices)
                this.vertices.map(data => head += data.data + " ") 
                head += "<tail>" 
                console.log(head)
            }

            }

and as you can see from my terminal look at the top! it shows Array.isarray(myarray) is true and console.log of this.vertices is the linkedlist then at the bottom it prints am empty array. However this.vertices prints the linkedList to the console enter image description here

Upvotes: 0

Calvin Mwadime
Calvin Mwadime

Reputation: 48

I had the same problem and when I logged the variable snapshot as shown below the variable was logged after most of the logic after it was executed, since it was available later, that is why the Array values are not accessible.

let admins = []
adminRef.once('value',(snapshot)=>{
   console.log(snapshot);
   snapshot.forEach(data=>{
   admins.push(data.key); 
 })
 })

So changed it so that the logic underneath was executed once the snapshot variable was available

 adminRef.once('value',(snapshot)=>{
        if(snapshot){
            console.log(snapshot);
            snapshot.forEach(data=>{
            admins.push(data.key); 
        })}

Upvotes: 1

safrazik
safrazik

Reputation: 1601

For anyone else who is facing similar issue:

You are very likely populating the array within an asynchronous function.

function asyncFunction(list){
 setTimeout(function(){
    list.push('a');
    list.push('b');
    list.push('c');
    console.log(list.length); // array length is 3 - after two seconds
 }, 2000); // 2 seconds timeout
}

var list=[];
//getting data from a database
asyncFunction(list);
console.log(list.length) //array is length zero - after immediately
console.log(list) // console will show all values if you expand "[]" after two seconds

Upvotes: 12

Roy J
Roy J

Reputation: 43899

__proto__ is not your object, it is the accessor for the prototype.

The __proto__ property of Object.prototype is an accessor property (a getter function and a setter function) that exposes the internal [[Prototype]] (either an object or null) of the object through which it is accessed.

The use of __proto__ is controversial, and has been discouraged.

Upvotes: 1

Dylan Wright
Dylan Wright

Reputation: 1212

I'd need to see more of your code but this is something that you'd want. 

var arr = [1, 3, 5, 6];
console.log(arr.length);
for (var i = 0; i < arr.length; i++){
  console.log(arr[i]);
}

Upvotes: 0

Related Questions