Polyfill of Reduce

Hi, friends
I am writing the polyfill of Reduce...
So those readers are not aware of what is Array.reduce please take a look at the MDN site.
Here is the Link :
Array.reduce()

So First I am sharing my whole code of custom Reduce function
then we will discuss the code Line by Line

Array.prototype.myReduce = function(callback, initalValue){

 // Start Handling of errors
 if(this==null || this==undefined) {
   return('The Array you passed is null or undefined')
 };

 if(!callback || typeof callback !== 'function') {
   return('callback not exist or not a function')
 };

 if(!this.length){
   if(arguments.length<2){
     return('Array is empty && intialValue is not given');
   }else{
     return(initalValue);
   }
 }
 // End of handling of errors

 if(this.length){
 var k = 0;
 var acc;
 if(arguments.length<2){
   acc = this[0];
   k++;
 }else if(arguments.length==2){
   acc = initalValue
 }

  while(k<this.length){
    acc = callback(acc, this[k]);
    k++;
  }
  return(acc);
 }
}

const sum = (a,b)=>{return a*b};
let result = [1,3].myReduce(sum, 5);
console.log(result);
result = [1,3,5].myReduce(sum, 4);
console.log(result);
result = [].myReduce(sum, 4);
console.log(result);
result = [1,2].myReduce(sum);
console.log(result);

Okay Now I am explaining the code

The first Condition is

if(this==null || this==undefined) {
   return('The Array you passed is null or undefined')
 };

Here this referring to the Array you passed... means if the Array you passes is null or undefined output should be an error...
for more use case you can check out the original Reduce function on the MDN site

Comments

[shadowtime2000]

Imagine you do this:

for (const i in myArray) {
console.log(i);
}

this would be the output:

someElem1
someElem2
myReduce

This is another basic snippet of code that has been shared around the internet a bit and you also didn't explain how it works.