Angular = array length is always 1?

Question

The following is the code in typescript,

count: number;

this.count is accessed from html component.

console.log(this.count) gives me 5.

var arrObj:number[] = new Array(this.count)

console.log(arrObj.length);

Here the length of the array is always 1.

var arrObj:number[] = new Array(5)

console.log(arrObj.length);

Output: 5

var arrObj:number[] = new Array(this.count)

console.log(arrObj.length);

Output:1

Why is the global variable length is always 1?

Akber Iqbal · Accepted Answer · 2019-03-13 06:33:48Z

0

An array can also be created using the Array object. The Array constructor can be passed.

A numeric value that represents the size of the array
or A list of comma separated values.
ref:https://www.tutorialspoint.com/typescript/typescript_arrays.htm

you are initializing the array again and again... from the code that you've shared, when you do:

var arrObj:number[] = new Array(5)
you're initializing the array of size 5 in this case, which will all be undefined

and when you do...

var arrObj:number[] = new Array(1)
you're initializing the array with a single item, which will be undefined in this case

you should do this once var arrObj:number[] = [] and then push the value in the array by doing arrObj.push(yourValue)

demo on stackblitz

edited Mar 13, 2019 at 6:33

answered Mar 12, 2019 at 4:57

Akber Iqbal

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1 Comment

Asha Latha Over a year ago

va arrobj:number[ ] =new Array(5) i.e; the array construtor is used.So when i pass 5 it creates an array of size 5 i.e; the length of the array(arrobj.length) gives me 5.. but i pass a variable which is global (this.count) and contains a value equals to 5 i.e; var arrobj:number[]=new Array(this.count ) give me an arrobj.length =1. Why is it so??

arpit sharma · Accepted Answer · 2019-03-13 08:19:53Z

0

'this' always works in scope and array constructor always accept static values it will never do eval(this.something), so when you pass 'this.count' it is passed as 1 undefined static value that is why it is becoming one length array(undefined being a static value in itself).
Also to be noted array constructor accepts only

A numeric value that represents the size of the array or
list of comma separated values.

In your case if you need alternate solution then initialize array empty and then assign
arrObj.length = this.count

answered Mar 13, 2019 at 8:19

arpit sharma

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