equalHeight.js

jQuery(document).ready(function($) { 
  
  let selector = $( '.selector' )
  
  // Get an array of all element heights
  var elementHeights = selector.map( function() {
    return $( this ).height();
  }).get()

  // Math.max takes a variable number of arguments
  // `apply` is equivalent to passing each height as an argument
  var maxHeight = Math.max.apply( null, elementHeights )

  // Set each height to the max height
  selector.height( maxHeight )
  
})