The update item with ajax does not affect until the end of the loop

Question

I want to print many ONE-BY-ONE numbers with AJAX.

something like this: (each new line updates the previous line!)

output is:
    1
    12
    123
    1234
    12345
    123456
    ...

I tried a lot and read a lot of the same problem, but I could not find my answer.

The real problem is that every FOR LOOP in javascript will NOT affect the DOM after it finishes the loop. I just want to update the DOM inside FOR LOOP while working on a long job.

Please see my code.

$("#btn").on("click", dowork);

function dowork() {
  document.getElementById("foo").innerHTML = "working";
  setTimeout(function() {
    var counter = 100; // i want assign counter = 2000000000
    for (var i = 0; i < counter; i++) {
      document.getElementById("print_here").innerHTML += i;
    }
    document.getElementById("foo").innerHTML = "done!";
  }, 50);
}

#btn {
  background: #1f1f1f;
  padding: 10px;
  font-weight: bolder;
  color: #fff;
  width: 50%;
  margin: auto;
  margin-top: 10px;
  text-align: center;
  cursor: pointer;
}

#print_here {
  overflow-wrap: break-word;
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<div id="btn">CLICK TO DO WORK</div>
<div id="foo"></div>
<div id="print_here"></div>

Run code

Thanks for any answer and help solve this problem.

Answer 1

DOM "", , . , DOM , DOM setTimeout, :

setTimeout(function(){
    document.getElementById("print_here").innerHTML += i;
},1);

, setTimeout i, let i var i

$("#btn").on("click", dowork);

function dowork() {
  document.getElementById("foo").innerHTML = "working";

  var counter = 3000; // i want assign counter = 2000000000
  for (let i = 0; i < counter; i++) {
    setTimeout(function() {
      document.getElementById("print_here").innerHTML += i;
    }, 1);
  }
  document.getElementById("foo").innerHTML = "done!";
}

#btn {
  background: #1f1f1f;
  padding: 10px;
  font-weight: bolder;
  color: #fff;
  width: 50%;
  margin: auto;
  margin-top: 10px;
  text-align: center;
  cursor: pointer;
}

#print_here {
  overflow-wrap: break-word;
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<div id="btn">CLICK TO DO WORK</div>
<div id="foo"></div>
<div id="print_here"></div>

#foo "done!" , FOR

, , setTimeout, :

if (i == counter - 1){
    document.getElementById("foo").innerHTML = "done!";
}

$("#btn").on("click", dowork);

function dowork() {
  document.getElementById("foo").innerHTML = "working";

  var counter = 3000; // i want assign counter = 2000000000
  for (let i = 0; i < counter; i++) {
    setTimeout(function() {
      document.getElementById("print_here").innerHTML += i;
      if (i == counter - 1){
        document.getElementById("foo").innerHTML = "done!";
      }
    }, 1);
  }
}

#btn {
  background: #1f1f1f;
  padding: 10px;
  font-weight: bolder;
  color: #fff;
  width: 50%;
  margin: auto;
  margin-top: 10px;
  text-align: center;
  cursor: pointer;
}

#print_here {
  overflow-wrap: break-word;
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<div id="btn">CLICK TO DO WORK</div>
<div id="foo"></div>
<div id="print_here"></div>

Answer 2

, , . , .

- setImmediate nextTick. , polyfill: https://www.npmjs.com/package/browser-next-tick

, , ... .

Answer 3

Here is the working code for you:

$("#btn").on("click", dowork);

function dowork() {
  document.getElementById("foo").innerHTML = "working";
  setTimeout(function() {

    var i, j, row = 5;
    var html = "";
    for (i = 1; i <= row; i++) {
      for (j = 1; j <= i; j++) {
        html += "<span>" + j + "</span>";
      }
      html += "</br>";
    }
    console.log(html);
    document.getElementById("print_here").innerHTML = html;
  }, 50);
}

#btn {
  background: #1f1f1f;
  padding: 10px;
  font-weight: bolder;
  color: #fff;
  width: 50%;
  margin: auto;
  margin-top: 10px;
  text-align: center;
  cursor: pointer;
}

#print_here {
  overflow-wrap: break-word;
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<div id="btn">CLICK TO DO WORK</div>
<div id="foo"></div>
<div id="print_here"></div>

Run code

Lines is the number of lines you want to print.