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JavaScript SyntaxError – Applying the ‘delete’ operator to an unqualified name is deprecated
  • Last Updated : 31 Jul, 2020

This JavaScript exception applying the ‘delete’ operator to an unqualified name is deprecated works in strict-mode and it occurs if variables are tried to be deleted with the delete operator.

Message:

SyntaxError: Calling delete on expression not allowed
             in strict mode (Edge)
SyntaxError: applying the 'delete' operator to an unqualified name
             is deprecated (Firefox)
SyntaxError: Delete of an unqualified identifier in strict mode. 
             (Chrome)

Error Type:

SyntaxError

Cause of Error: In strict mode, trying to delete a variable will throw an error and is not permitted. Normal variables in JavaScript can’t be deleted with help of the delete operator. 

Example 1:



HTML




<!DOCTYPE html>
<html>
<head>
    <title>Syntax Error</title>
</head>
<body>
    <script>
      'use strict';
      var GFG ="This is GeeksforGeeks";
      document.write(GFG);
      GFG = null; 
    </script>
</body>
</html>

Output:

This is GeeksforGeeks

Example 2: In this example, delete operator is used which causes the error.

HTML




<!DOCTYPE html>
<html>
<head>
    <title>Syntax Error</title>
</head>
<body>
    <script>
      'use strict';
      var GFG ="This is GeeksForGeeks";
      document.write(GFG);
      delete GFG; 
    </script>
</body>
</html>

Output(in console):

SyntaxError: Delete of an unqualified identifier in strict mode.
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