Auto Convert of int to string when pushed it to array

Question

Suppose I have a array like that:

let array = [1, 45, 14, 4]

When I look for the type of these integers I get a number type (Normal: Exactly what i expected )

Now suppose that I declare my array like that :

let array = [].push(1) or [].concat([1,2,3])

Now, If I try to get the type with "typeof", I get a type of string

In the snippets below all integers in an array are of string types. I do not understand why!

PS: I need the types to be strict

 var array = [1,2,3,4,5]; for (item in array) { console.log(typeof item); } 

Answer 1

They are numbers

 var array = [1,2,3,4,5]; array.push(6); array = array.concat([7,8,9]) for(var i = 0; i < array.length; i++) { console.log(typeof array[i]) } 

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And if you check the item 's value in your sample, you'll see it is not the array items, it is their index, which is how for/in works when iterate an object (which an array actually is too)

 var array = [1,2,3,4,5]; for(item in array) { console.log(typeof item, "type, and item value is: " + item) } 

Answer 2

Here for..in loop iterates over keys and it is the index of element in string format. Hence the type here is string for each element's key.

While typeof array element is obviously number. Check it in below code:

 var array = [1,2,3,4,5]; for(item in array) { console.log(typeof item, item, typeof array[item], array[item]) } 

Answer 3

As others stated the for...in statement enumerates the property names (the keys) of an object, which are string here

As CRice suggested you can use the forEach method to enumerate the array 's members.

 var array = [1,2,3,4,5]; array.forEach(function(item){ console.log(typeof item) }); 

Answer 4

You made small mistake, for(i in arr) giving you not item but index

 var array = [1, 2, 3, 4, 'a']; for(idx in array){ //console.log(typeof array[i]) console.log('index:'+idx+ ' item:'+array[idx]+ ' typeof:'+typeof array[idx]) } 

Or you can use for loop like that to have directly access to item:

 var array = [1, 2, 3, 4, 'a']; for (var idx = 0; idx < array.length; idx++) { console.log(array[idx]+':'+typeof array[idx]) } 

Third option is to use forEach():

 var array = [1, 2, 3, 4, 'a']; array.forEach( item=> console.log(item+':'+typeof item) )