# JavaScript: Get n random elements at unique keys from array up to the size of array

## JavaScript fundamental (ES6 Syntax): Exercise-226 with Solution

Write a JavaScript program to get n random elements at unique keys from array up to the size of array.

• Shuffle the array using the Fisher-Yates algorithm.
• Use Array.prototype.slice() to get the first n elements.
• Omit the second argument, n, to get only one element at random from the array.

Sample Solution:

JavaScript Code:

``````//#Source https://bit.ly/2neWfJ2
const sampleSize = ([...arr], n = 1) => {
let m = arr.length;
while (m) {
const i = Math.floor(Math.random() * m--);
[arr[m], arr[i]] = [arr[i], arr[m]];
}
return arr.slice(0, n);
};

console.log(sampleSize([1, 2, 3], 2));
console.log(sampleSize([1, 2, 3], 4));
```
```

Sample Output:

```[3,2]
[2,3,1]
```

Pictorial Presentation:

Flowchart:

Live Demo:

See the Pen javascript-basic-exercise-226-1 by w3resource (@w3resource) on CodePen.

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## JavaScript: Tips of the Day

How to check whether a string contains a substring in JavaScript?

ECMAScript 6 introduced String.prototype.includes:

```const string = "foo";
const substring = "oo";

console.log(string.includes(substring));
```

includes doesn't have Internet Explorer support, though. In ECMAScript 5 or older environments, use String.prototype.indexOf, which returns -1 when a substring cannot be found:

```var string = "foo";
var substring = "oo";

console.log(string.indexOf(substring) !== -1);
```

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