The Array.reduce() is an inbuilt TypeScript function which is used to apply a function against two values of the array as to reduce it to a single value. 
Syntax:
array.reduce(callback[, initialValue])
Parameter: This method accept two parameter as mentioned and described below:
- callback : This parameter is the Function to execute on each value in the array.
 - initialValue : This parameter is the Object to use as the first argument to the first call of the callback.
 
Return Value: This method returns the reduced single value of the array. 
Below examples illustrate the  Array reduce() method in TypeScript
Example 1:
JavaScript
<script>     // Driver code     var arr = [ 11, 89, 23, 7, 98 ];        // use of reduce() method      var val = arr.reduce(function(a, b)     {          return a + b;      });            // printing element     console.log( val ); </script> | 
Output:
228
Example 2:
JavaScript
<script>     // Driver code     var arr = [2, 5, 6, 3, 8, 9];      var val;        // use of reduce() method      val = arr.reduce(function(a, b)     {          return a*b/2;      });            // printing element     console.log( val ); </script> | 
Output:
405
