CODEWITHSUNDEEP
javascriptarraystypescript
karansys
karansys

Reputation: 2719

How to print array elements?

I am trying to print array element to console using for each loop in javascript. But I am printing something which I am not able to figure out what!

 let arr=["1,2,3","iosajah","undefined"];
    for(let data in arr)
    { 
        console.log(data);// prints 4,0,1,2 
        if(typeof data === "undefined")
        {
          //do something

        }
    }

console.log(data) prints 4,0,1,2

but I expected it to print each array element

Upvotes: 3

Views: 21645

Answers (5)

carter
carter

Reputation: 5432

I have changed data to key since that is what the for... in... syntax produces: the key of the object (which may be an Array) during the iteration. You should not have printed a 4 at all as this typescript playground shows: Typescript Playground Example

 let arr=["1,2,3","iosajah","undefined"];
 for(let key in arr)
 { 
     console.log(arr[key]);// prints 0,1,2 
     if(typeof arr[key] === "undefined")
     {
          //do something

     }
 }

If you want to iterate over an array the more typical way to do it is using the .forEach syntax.

let arr=["1,2,3","iosajah","undefined"];
arr.forEach((element, index, arr) => {
    console.log(element, index);
    if (typeof element === "undefined") {
        //do something
    }
})

It also looks like you probably are intending to look for the string undefined in the array and if that is the case then you don't want to check the typeof, you just want to compare the string value:

if (element === "undefined") {

}

The typeof element will never be a string of value "undefined" in this example.

Upvotes: 1

Nina Scholz
Nina Scholz

Reputation: 386560

You could take a for ... of statement where you get the element instead of the for ... in statement where you get the indices of the array.

Difference between for...of and for...in

Both for...in and for...of statements iterate over something. The main difference between them is in what they iterate over.

The for...in statement iterates over the enumerable properties of an object, in an arbitrary order.

The for...of statement iterates over values that the iterable object defines to be iterated over.

let arr = ["1,2,3", "iosajah", "undefined"];
for (let data of arr) {
    console.log(data);
}

To get the elements in the order of the indices, you could take a standard for statement and go from the first element to the end of the array.

let arr = ["1,2,3", "iosajah", "undefined"];
for (let i = 0; i < arr.length; i++) {
    console.log(arr[i]);
}

Upvotes: 1

Dupocas
Dupocas

Reputation: 21307

for in loops over enumerable property names of an object, you are printing the indexes of the array. If you want to iterate over the values use one of the approaches:

for(let value of array)

Or

Object.keys(array).map(key => console.log(array[key]))

Upvotes: 3

shadow2020
shadow2020

Reputation: 1351

Your For/In statement is to traverse properties of an object. If you check the length of your array and step through it. We want values, rather than properties. You can print it this way. 

let arr=["1,2,3","iosajah","undefined"];
    for(i=0;i<arr.length;i++)
      {
       console.log(arr[i]);
       if(typeof data === "undefined"){
       //do something
      }
    }

Upvotes: 1

JohnSnow
JohnSnow

Reputation: 454

for in loop is used to iterate through object literals, but since Arrays (and everything else) are actually objects in JavaScript you are actually logging the keys of the Array object which are the index values.

You want to use forEach

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/forEach

let arr=["1,2,3","iosajah","undefined"];

arr.forEach(function(element) {
  console.log(element);
});

Upvotes: 1

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