Detailed explanation of the use of reduce() method in JavaScript

The JavaScript array reduce() method applies a function to two values ​​of the array (from left to right) simultaneously to reduce them to one value.
Syntax

array.reduce(callback[, initialValue]);

The following are the details of the parameters:

callback: function is executed on each value in the array

initialValue: object as The first callback of the first parameter callback uses

Return value:

Returns a reduced single value of the array
Compatibility:

This method is a JavaScript extends to the ECMA-262 standard; therefore it may not exist in other implementations of the standard. In order for it to work, you need to add the following script to the top of the code:

if (!Array.prototype.reduce)
{
 Array.prototype.reduce = function(fun /*, initial*/)
 {
  var len = this.length;
  if (typeof fun != "function")
   throw new TypeError();
 
  // no value to return if no initial value and an empty array
  if (len == 0 && arguments.length == 1)
   throw new TypeError();
 
  var i = 0;
  if (arguments.length >= 2)
  {
   var rv = arguments[1];
  }
  else
  {
   do
   {
    if (i in this)
    {
     rv = this[i++];
     break;
    }
 
    // if array contains no values, no initial value to return
    if (++i >= len)
     throw new TypeError();
   }
   while (true);
  }
 
  for (; i < len; i++)
  {
   if (i in this)
    rv = fun.call(null, rv, this[i], i, this);
  }
 
  return rv;
 };
}

Example:

This will produce the following results:

total is : 6

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