 # JavaScript: Find whether the members of a given array of integers is a permutation of numbers from 1 to a given integer

## JavaScript Basic: Exercise-123 with Solution

Write a JavaScript program to find whether the members of a given array of integers is a permutation of numbers from 1 to a given integer.

Pictorial Presentation: Sample Solution:

HTML Code:

``````<!DOCTYPE html>
<html>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width">
<title> Find whether the members of a given array of integers is a permutation of numbers from 1 to a given integer</title>
<body>

</body>
</html>
```
```

JavaScript Code:

``````function is_permutation(input_arr, n) {
for (var i = 0; i < n; i++) {
if (input_arr.indexOf(i + 1) < 0)
return false;
}
return true;
}
console.log(is_permutation([1, 2, 3, 4, 5], 5));
console.log(is_permutation([1, 2, 3, 5], 5));
``````

Sample Output:

```true
false
```

Flowchart: ES6 Version:

``````function is_permutation(input_arr, n) {
for (let i = 0; i < n; i++) {
if (!input_arr.includes(i + 1))
return false;
}
return true;
}
console.log(is_permutation([1, 2, 3, 4, 5], 5));
console.log(is_permutation([1, 2, 3, 5], 5));
``````

Live Demo:

See the Pen javascript-basic-exercise-123 by w3resource (@w3resource) on CodePen.

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## JavaScript: Tips of the Day

Parameter's value

```function getItems(fruitList, ...args, favoriteFruit) {
return [...fruitList, ...args, favoriteFruit]
}

getItems(["banana", "apple"], "pear", "orange")
```

...args is a rest parameter. The rest parameter's value is an array containing all remaining arguments, and can only be the last parameter! In this example, the rest parameter was the second parameter. This is not possible, and will throw a syntax error.

```function getItems(fruitList, favoriteFruit, ...args) {
return [...fruitList, ...args, favoriteFruit];
}

getItems(['banana', 'apple'], 'pear', 'orange');```
The above example works. This returns the array [ 'banana', 'apple', 'orange', 'pear' ].

Ref: https://bit.ly/3jFRBje