javascript Map and Reduce examples

ES6-Map-Reduce.js

let selector,
    $elements,
    testsPassed,
    totalTestsPassed;
    
// Select the 7th <td> from every <tr>, excluding the first <tr>
selector = '#testresult tr:not(:first-child) td:nth-child(7)';

// Get array of selected elements
$elements = $$ 
  ? $$(selector) // Prototype selector
  : document.getElementBySelector(selector) // Pure JS selector

// Map counts from $elements innerHTML to a new array
testsPassed = $elements.map( $el => parseInt($el.innerHTML) );

// Reduce the list of numbers to their sum
totalTestsPassed = testsPassed.reduce((left, right) => left + right);

// Condensed
totalTestsPassed = document.getElementsBySelector('#testresult tr:not(:first-child) td:nth-child(7)')
                           .map( $el => parseInt($el.innerHTML) )
                           .reduce((left, right) => left + right);

/* Using just the reduce function with consideration for left's type change after the first iteration
      Pass 1: reduce($el[0], $el[1]) => total   // [Object, Object] => Int
      Pass 2: reduce(total,  $el[2]) => total   // [Int, Object] => Int
*/
totalTestsPassed = document.getElementsBySelector('#testresult tr:not(:first-child) td:nth-child(7)')
                           .reduce( (left, right) => parseInt(left.innerHTML || left) + parseInt(right.innerHTML) );