Basic usage of reduce function

Grammar:

arr.reduce(callback,[initialValue])
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What it does: Receives a function as an accumulator that executes callbacks for each element in an array, excluding elements that were deleted or never assigned, and takes four arguments: the initial value (the value returned by the last callback), the current element value, the current index, and the original array

Simple example: Add all the values in an array

    // Define a set of numbers
    let nums = [10.20.30.40.50];
    let total = nums.reduce(function(preValue, n) {
      //return The sum of the two values
      return preValue + n
      //preValue Sets the initial value to 0
}, 0)
    // Prints 150
    console.log(total)
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Note: preValue is the last return value: