Array reduce() Method

The Array reduce() method returns a single value after iterating through each element of the given array inside the user-supplied callback function, where some calculation is performed on the preceding element. The syntax for this method is

				
				array.reduce(callback(accumulator, currentValue), initialValue)

The callback() function has two arguments as follows:

accumulator

The value returned in the previous call to the callback() function. Initially, it holds the second parameter initialValue if it is passed, else, it takes the value array[0].

currentValue

Index of the current element in the array.

The second parameter initialValue (optional) is the value passed to the callback() on first call.

In this simple example below, we will join the words in the given array and create a full sentence.

					
					let arr = ["I", "am", "worried", "about", "Gort"];
					let say = arr.reduce((acc, i) => acc + " " + i);
					
					console.log(say); // I am worried about Gort

Now we pass a string "Klaatu:" as the initialValue, which makes the value of the accumulator initially.

					
					let arr = ["I", "am", "worried", "about", "Gort"];
					let say = arr.reduce((acc, i) => acc + " " + i, "Klaatu: ");
					
					console.log(say); // Klaatu: I am worried about Gort