# JavaScript: Get the highest index at which value should be inserted into array in order to maintain its sort order

## JavaScript fundamental (ES6 Syntax): Exercise-141 with Solution

Write a JavaScript program to get the highest index at which value should be inserted into an array in order to maintain its sort order.

• Loosely check if the array is sorted in descending order.
• Use Array.prototype.reverse() and Array.prototype.findIndex() to find the appropriate last index where the element should be inserted.

Sample Solution:

JavaScript Code:

``````//#Source https://bit.ly/2neWfJ2

// Define the 'sortedLastIndex' function
const sortedLastIndex = (arr, n) => {
// Determine if the array is sorted in descending order
const isDescending = arr[0] > arr[arr.length - 1];
// Find the index where 'n' should be inserted into the sorted array
const index = arr
.reverse() // Reverse the array to search from the end
.findIndex(el => (isDescending ? n <= el : n >= el)); // Find the index based on sorting order
// Return the index after adjusting for the reversed array and considering array length
return index === -1 ? 0 : arr.length - index;
};

// Test the 'sortedLastIndex' function
console.log(sortedLastIndex([10, 20, 30, 30, 40], 30)); // Output: 4
```
```

Output:

```4
```

Flowchart:

Live Demo:

See the Pen javascript-basic-exercise-141-1 by w3resource (@w3resource) on CodePen.

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