# JavaScript: Initializes an array containing the numbers in the specified range (in reverse) where start and end are inclusive with their common difference step

## JavaScript fundamental (ES6 Syntax): Exercise-214 with Solution

Write a JavaScript program to initialize an array containing the numbers in the specified range (in reverse) where start and end are inclusive of their common difference step.

• Use Array.from(Math.ceil((end+1-start)/step)) to create an array of the desired length(the amounts of elements is equal to (end-start)/step or (end+1-start)/step for inclusive end), Array.prototype.map() to fill with the desired values in a range.
• Omit the second argument, start, to use a default value of 0.
• Omit the last argument, step, to use a default value of 1.

Sample Solution:

JavaScript Code:

``````// Define a function 'initializeArrayWithRangeRight' that creates an array filled with a range of numbers, starting from 'start' (default: 0) to 'end' (inclusive), with a specified 'step' (default: 1), in reverse order
const initializeArrayWithRangeRight = (end, start = 0, step = 1) =>
// Create an array of length equal to the number of elements in the range using 'Array.from'
Array.from({ length: Math.ceil((end + 1 - start) / step) })
// Map each element in the array to the corresponding value in the range, starting from 'end' and decrementing by 'step'
.map((v, i, arr) => (arr.length - i - 1) * step + start);

// Test the 'initializeArrayWithRangeRight' function by creating arrays filled with ranges of numbers in reverse order
console.log(initializeArrayWithRangeRight(5));
// Output: [5, 4, 3, 2, 1, 0]
console.log(initializeArrayWithRangeRight(7, 3));
// Output: [7, 6, 5, 4, 3]
console.log(initializeArrayWithRangeRight(9, 0, 2));
// Output: [8, 6, 4, 2, 0]
```
```

Output:

```[5,4,3,2,1,0]
[7,6,5,4,3]
[8,6,4,2,0]
```

Visual Presentation:

Flowchart:

Live Demo:

See the Pen javascript-fundamental-exercise-214 by w3resource (@w3resource) on CodePen.

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