[Solved] Could you help me Explain what this means?

by 


var list=["https://stackoverflow.com/questions/37702877/Red.jpg","Amber.jpg","Green.jpg","AmberLast.jpg"];

this is an array of names of image sources.

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array

  var index = 0;

this a variable, it’s called index, and has the value of 0 because you can target an element of an array (e.g Amber.jpg) using it’s index. An array’s index by default starts at 0 (zero based), so in the ‘list’ array above, the index of 0 (list[0]) will return “https://stackoverflow.com/questions/37702877/Red.jpg”.

  function changeLights() {

    var image = document.getElementById("https://stackoverflow.com/questions/37702877/Red.jpg");
    var display = document.getElementById('display');
    index = (index + 1) % 4;
    image.src = list[index];
    display.innerHTML = list[index];

  }

This function selects the <img> tag with the ID of “https://stackoverflow.com/questions/37702877/Red.jpg”, and then sets it’s src= to be index + 1 (= 1), and then sets the inner HTML of the element with an ID of display to be Amber.jpg (list[1]).

The correct way to ‘change lights’ would instead be: 

var list=["https://stackoverflow.com/questions/37702877/Red.jpg","Amber.jpg","Green.jpg","AmberLast.jpg"];

var index = 0;

function changeLights() {

   var max = list.length - 1;
   var next = index += 1; 

   if(next > max) {
      next = 0; //start back at beginning
      index = 0;
   }  

   var image = document.getElementById('IDOFIMAGETAG'); //replace will correct ID of <img>

   image.src = list[next];

}

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solved Could you help me Explain what this means?