Array.prototype.sample.js

Array.prototype.sample = function(count = 1){
	let {length} = this;
	if( count > length ){
		count = length;
	}
	return this.map( (item, idx) => {
			return {item, rnd: Math.random()};
		})
		.sort( (a, b) => a.rnd - b.rnd )
		.slice( length - count )
		.map( item => item.item );
}

Array.prototype.sample.v2.js

Array.prototype.sample = function(count = 1){
	let {length} = this;
	if( count > length ){
		count = length;
	}
	let result = [];
	while(result.length < count) {
		let idx = Math.floor(length * Math.random());
		if(result.indexOf(idx) === -1){
			result.push(idx);
		}
	}
	return this.filter( (item, idx) => result.indexOf(idx) !== -1 );
}