![]() So, assign a value immediately after declaration. The best way to solve uninitialized variables issues is by assigning an initial value whenever possible. This is a declared variable that is yet to be assigned a value, and by default, it is undefined. ![]() The Creation of Undefined: How Does Undefined Occur?īelow are scenarios that lead to undefined. Undefined type – it is a type having a single value, undefined. So when you access uninitialized variables, you receive undefined. Undefined value –a primitive value utilized when a variable hasn’t been assigned a value. But it is not a good idea because it makes the code tricky to maintain and debug. You can make undefined an identifier in all scopes but not global scope. This JavaScript primitive type lacks objects and methods and is automatically assigned to a declared variable or a formal argument lacking the actual arguments.Īlso, a method or a statement can return undefined, but the evaluated variable must not have a value. Its initial value is the primitive value undefined. Typically, undefined is a variable in global scope, i.e., a property of the global object. Undefined means that there is no value assigned to a variable – not declared. JavaScript undefined – A Straightforward Definition Void and typeof are much faster than direct comparison against undefined. Using void 0 is much easier and quicker if you know what it means – the above code is clear and concise. For instance, xyz = void 0 is slightly faster in chrome than typeof. However, the browser of choice may influence results. However, others prefer typeof because it is the safest and less error-prone method to check for undefined JavaScript values. Some users prefer xyz = undefined as it is clearer. The various techniques produce results with negligible differences. JavaScript checking for undefined is pretty straightforward regardless of the method. That explains the different techniques to check for undefined. JavaScript is constantly adding new capabilities for easy usage. – Direct Comparison of a Variable to Undefined. ![]()
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