How to check whether i submit blank input in javascript? i have written a program but it is not working

Question

I have written a javascript code in an HTML file using a script tag, where I want to know whether my input is greater than or less than 10 or equals to 10 or any blank input. I use the if-else method to solve this problem, but my last else if condition which is "Your input is blank" not outputting in any way.

//f1 function will run when some hit the submit button
function f1() {
  //here we are taking the value of the input field using id "myinput" in the variable called myinputvar
  var myinputvar = document.getElementById("myinput").value;
  if (myinputvar > 10) {
    document.getElementById("txt").innerHTML = "Your input number is greater than 10";
  } else if (myinputvar < 10) {
    document.getElementById("txt").innerHTML = "Your input number is less than 10";
  } else if (myinputvar = 10) {
    document.getElementById("txt").innerHTML = "Your input number is 10";
  } else if (myinputvar = " ") {
    document.getElementById("txt").innerHTML = "Your input is blank";
  }
}

<!-- this is the input tag to take inputs from user -->
Enter a integer number between 0 to anynumber = <input type="text" id="myinput"><br><br>
<!-- this is the button to submit the value -->
<button onclick="f1()">submit</button>
<!-- this is the heading tag to print the output -->
<h1 id="txt"></h1>

Answer 1

Wrap in a form and make it required

Also cast to number

document.getElementById("myForm").addEventListener("submit", function(e) {
  e.preventDefault(); // stop submission
  //here we are taking the value of the input field using id "myinput" in the variable called myinputvar
  var myinputvar = +document.getElementById("myinput").value; // make it a number
  if (myinputvar > 10) {
    document.getElementById("txt").innerHTML = "Your input number is greater than 10";
  } else if (myinputvar < 10) {
    document.getElementById("txt").innerHTML = "Your input number is less than 10";
  } else if (myinputvar = 10) {
    document.getElementById("txt").innerHTML = "Your input number is 10";
  } else if (myinputvar = " ") {
    document.getElementById("txt").innerHTML = "Your input is blank";
  }
})

<form id="myForm">
  Enter a integer number between 0 to anynumber =
  <input type="text" required id="myinput"><br><br>
  <button>submit</button>
</form>
<h1 id="txt"></h1>