How to tell if a <script> tag failed to load?

The problem is to identify whether the passed script loaded successfully or not using JavaScript. There are two methods which are discussed below:

Approach 1:

  • Set a variable loaded = false.
  • Pass the URL of the JavaScript file in the <script> tag.
  • Set the onload parameter, if script loaded set loaded = true.

Example:This example illustrate the approach discussed above.



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<!DOCTYPE HTML> 
<html
  
<head
    <title
        How to tell if a script tag failed
        to load in JavaScript ?
    </title>
      
    <script>
        var loaded = false;
    </script>
      
    <script src=
                onload="loaded=true;" >
    </script>
</head
  
<body style = "text-align:center;"
      
    <h1 style = "color:green;"
        GeeksgorGeeks 
    </h1>
      
    <p id = "GFG_UP" style
        "font-size: 15px; font-weight: bold;">
    </p>
      
    <button onclick = "gfg_Run()"
        Click here
    </button>
      
    <p id = "GFG_DOWN" style =
        "font-size: 23px; font-weight: bold; color: green; ">
    </p>
      
    <script>
        var el_up = document.getElementById("GFG_UP");
        var el_down = document.getElementById("GFG_DOWN");
          
        el_up.innerHTML = "Click on the button to check "
                    + "whether script is loaded or not."; 
          
        function gfg_Run() {
            if(loaded) {
                el_down.innerHTML = "Loaded Successfully!";
            }
            else {
                el_down.innerHTML = "Not loaded!";
            }
        }         
    </script
</body
  
</html>

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Output:

  • Before clicking on the button:
  • After clicking on the button:

Approach 2:

  • Set a variable loaded = false.
  • Pass the URL of JavaScript file in a <script> tag.
  • Set the onload parameter, Trigger alert if script loaded.
  • If not then check for loaded variable, if it is equal to false, then script not loaded.

Example: This example follows the approach discussed above.

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<!DOCTYPE HTML> 
<html
  
<head
    <title
        How to tell if a script tag failed
        to load in JavaScript ?
    </title>
      
    <script>
        var loaded = false;
    </script>
      
    <script src="" 
        onload="alert('Script loaded!'); loaded=true;" >
    </script>
</head
  
<body style = "text-align:center;" id = "body"
      
    <h1 style = "color:green;"
        GeeksforGeeks 
    </h1>
      
    <p id = "GFG_UP" style
            "font-size: 15px; font-weight: bold;">
    </p>
      
    <script>
        var el_up = document.getElementById("GFG_UP");
        el_up.innerHTML = "Click on the refresh button "
            + "to check whether script is loaded or not.";
          
        if(!loaded) {
            alert("Script not loaded!");
        }
    </script
</body
  
</html>

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Output:

  • Before clicking on the button:
  • After clicking on the refresh button:


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