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)
delete operator. In strict mode, an attempt to delete a variable will throw an error and is not allowed.
delete operator can only delete properties on an object. Object properties are "qualified" if they are configurable.
Unlike what common belief suggests, the
delete operator has nothing to do with directly freeing memory. Memory management is done indirectly via breaking references, see the memory management page and the
delete 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