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)
operator. In strict mode, an attempt to delete a variable will throw an error and is not allowed.
operator can only delete properties on an object. Object properties are "qualified" if they are configurable.
Unlike what common belief suggests, the
to do with directly freeing memory. Memory management is done indirectly via breaking references, see the
page and the
operator page for more details.
This error only happens in
strict mode code
. In non-strict code, the operation just returns
'use strict'; var x; // ... delete x; // SyntaxError: applying the 'delete' operator to an unqualified name // is deprecated
To free the contents of a variable, you can set it to
'use strict'; var x; // ... x = null; // x can be garbage collected