JavaScript lastIndexOf(): Get the Last Index of an Element

The JavaScript lastIndexOf() method returns the last index of a specified element in a specified array. For example:

HTML with JavaScript Code
<!DOCTYPE html>
<html>
<body>

   <p id="xyz"></p>

   <script>
      const cities = ["Tokyo", "Los Angeles", "Bangkok", "Dubai", "Los Angeles", "Berlin"];
      let x = cities.lastIndexOf("Los Angeles");
      document.getElementById("xyz").innerHTML = x;
   </script>
   
</body>
</html>
Output

In the above example, the following JavaScript statement:

let x = cities.lastIndexOf("Los Angeles");

states that the index number of the last Los Angeles from the array named cities will initialize a variable named x.

Note: Indexing always starts with 0. Therefore, Tokyo is at index number 0. Similarly, the first Los Angeles is at index number 1, and the last Los Angeles is at index number 4.

JavaScript lastIndexOf() syntax

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

array.lastIndexOf(item, start)

Note: The item parameter is required and is used to specify the value that has to be searched in the array.

Note: The start parameter is optional and is used to specify where to start the search. The default value of this parameter is the index of the last element that is array.length-1.

Note: The lastIndexOf() method returns -1 if the specified value does not exist in the given array.

JavaScript lastIndexOf() example

Following is another example demonstrating the lastIndexOf() method in JavaScript:

HTML with JavaScript Code
<!DOCTYPE html>
<html>
<body>

   <p id="abc"></p>

   <script>
      const myarray = ["Tokyo", "Bangkok", "Tokyo", "Dubai", "Berlin", "Tokyo", "Frankfurt"];
      let lio = myarray.lastIndexOf("Tokyo", 3);
      document.getElementById("abc").innerHTML = lio;
   </script>
   
</body>
</html>
Output

If I remove 3 (the value of the start parameter), then the output should be 5. Because the last Tokyo is at index number 5. But since I specified 3, that's where to start the search. Therefore, the last Tokyo before index number 3 is available at index number 2.

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