created reduceFunction

reduce.js

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+/*
+ Do NOT use .reduce to complete this function.
+
+How reduce works: A reduce function combines all elements into a single value going from left to right.
+Elements will be passed one by one into `cb` along with the `startingValue`.
+`startingValue` should be the first argument passed to `cb` 
+  the array element should be the second argument.
+`startingValue` is the starting value.  If `startingValue` is undefined then make `elements[0]` the initial value.
+
+*/
+
+
+function reduce(elements, cb, startingValue) {
+
+     let index=0;
+
+     /* we will check if startingValue is undefined so we will start our 
+     loop from index=1 and will use first element of array as starting value
+      
+     if startingValue is not undefined our loop will start from index=0;
+     */
+     if(startingValue===undefined){
+
+        index=1;
+        startingValue=elements[0];
+       }
+
+     let accumulator=startingValue;
+
+     for(;index<elements.length;index++){
+
+        accumulator=cb(accumulator,elements[index],index);
+     }
+
+     return accumulator;
+}
+
+module.exports=reduce;

test/testReduce.js

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+const reduceFunc=require('../reduce');
+
+const items = [1, 2, 3, 4, 5, 5];
+
+
+function sumFunc(accumulator,curElement,index){
+
+    console.log("accumulator Current Value : ",accumulator)
+    return accumulator=accumulator+curElement;
+}
+
+let sumOfArrayElements=reduceFunc(items,sumFunc);
+
+console.log("Sum of Array's Element: "+sumOfArrayElements);