JavaScript entries(): Convert an Array to an Iterator Object

The JavaScript entries() method returns an object Array Iterator that will obviously have key/value pairs. For example:

HTML with JavaScript Code

<!DOCTYPE html>
<html>
<body>
   
   <script>
      const a = ["Berlin", "Vancouver", "Tokyo", "NYC"];

      const b = a.entries();
      
      for(let x of b)
      {
         document.write(x);
         document.write("<BR>");
      }
   </script>
   
</body>
</html>

The snapshot given below shows the sample output produced by the above JavaScript example:

Note: The for...of loop is used to loop through the values of an iterable object.

The code below declares a constant variable a and initializes it with an array of four string elements from the preceding example.

const a = ["Berlin", "Vancouver", "Tokyo", "NYC"];

The entries() function is called on the "a" array, and it returns a new iterator object containing the array's key/value pairs.

const b = a.entries();

To iterate over the b iterator object, a for..of loop is used. The loop variable x is assigned a key/value pair from the iterator object on each iteration.

for(let x of b)
{
   document.write(x);
   document.write("<BR>");
}

The document.write() method is used within the loop to display the current x value on the webpage. The entries() function returns an iterator that provides key/value pairs, resulting in a series of arrays, each containing the index and value of the corresponding element in the "a" array.

JavaScript entries() Syntax

The syntax of the entries() method in JavaScript is:

array.entries()

Advantages of the entries() function in JavaScript

The entries() function makes it simple to iterate over an object's or map's keys and values.
All modern browsers support the entries() function, so it is a safe method to use in your JavaScript code.
The entries() function works with arrays, maps, and objects, among other data types.

Disadvantages of the entries() function in JavaScript

If you need to support older browsers, you may need to use a polyfill or an alternative method since older browsers do not support the entries() function.
For large objects or maps, the entries() function can be memory-intensive because it creates a new array of key-value pairs.
When you need to access specific keys or values in an object or map, the entries() function might not be the best option. In those circumstances, it might be preferable to use different techniques, like Object.keys() or Map.get().

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