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

Last Updated : 17 Sep, 2019

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.

<!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= 
"https://ajax.googleapis.com/ajax/libs/jquery/3.4.1/jquery.min.js"
                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> 

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.

<!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> 

Output:

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

My Personal Notes

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