Reduce

by Aqilah Misuary

HTML

<p>
The reduce method is most often used to summarize values in arrays. For example:
[1,2,3,4,5].reduce(function(a,b){return a+b}); 
// ==> 15
</p>

<p>
To reduce an array, the comparison function must search in the previous array for the value and a.push(b) if it isn't already there and then return a;
</p>

<p>
The comparison function should therefore always return an array.
</p>

JavaScript

//REMOVE THE DUPLICATES 

var playLog = ['Madonna', 'Coldplay', 'Prince', 'Madonna', 'Madonna', 'Prince'];

var playHistory = playLog
.reduce(function(a,b){
	// return a combined version of a and b if not b is already in a
	
	if (a.indexOf(b) < 0 ) {
		a.push(b);
	}
    return a;
	
}, []); // this means that the initial 'a' will be an empty array

console.log(playHistory);