Array reduce()

In this chapter you will learn:

How to reduce array to a value

Array reduce()

reduce() is reduction method. reduce() iterates all items and build up a value for return. reduce() starts at the first item and traveling toward the last.

reduce() accepts two arguments:

a function to call on each item
an optional initial value

The function passed into reduce() accepts four arguments:

the previous value,
the current value,
the item's index,
the array object.

The returned value from the function is passed in as the first argument for the next item. The first iteration occurs on the second item in the array.

<!DOCTYPE html><!--from   j  a va 2  s.  c  o m-->
<html>
<head>
    <script type="text/javascript">
        var values = [1,2,3,4,5]; 
        
        var sum = values.reduce(function(prev, cur, index, array){
            return prev + cur; 
        }); 
        
        document.writeln(sum); //15 
       
    </script>
</head>
<body>
</body>
</html>

Click to view the demo

Next chapter...

What you will learn in the next chapter:

How to reduce a Javascript array from the end

Array reduce()

Array reduce()

Next chapter...

Array Type

Array creation

Array type detecting

Array iterate

Array Length

Add to Array

Array join

Array concat()

Array every method

Array search from start with indexOf()

Array search from the end with lastIndexOf()

Array filter

Array mapping

Array forEach

Array pop and push

Array shift()

Array reduce()

Array reduceRight()

Array reverse()

Array slice()

Array some()

Array splice()

Array sort()

Array toString()

Array unshift()