Can a variable be undefined?
undefined is a property of the global object. That is, it is a variable in global scope. A variable that has not been assigned a value is of type undefined . A method or statement also returns undefined if the variable that is being evaluated does not have an assigned value.
What is the difference between declaring a variable and assigning a variable?
Difference between Declaration, Initialization and Assignment. Initialization: When you declare a variable it is automatically initialized, which means memory is allocated for the variable by the JavaScript engine. Assignment: This is when a specific value is assigned to the variable.
When to use undefined when accessing uninitialized variables?
The standard clearly defines that you will receive undefined when accessing uninitialized variables, non-existing object properties, non-existing array elements, and alike. The above example demonstrates that accessing: a non-existing object property movie.year
What happens when a variable is undefined in JavaScript?
When something is undefined it is nothing.. it is not an object, neither a string, because it hasn’t been defined yet.. obviously.. then it is simply a property with no function.. You declare a variable with var but never set it.
What does it mean to have undefined behavior in C + +?
Undefined behavior is the result of executing code whose behavior is not well defined by the C++ language. In this case, the C++ language doesn’t have any rules determining what happens if you use the value of a variable that has not been given a known value.
When do I initialize variables in JavaScript with null?
It is commonly used to clear a value already stored in an existing variable. It could be seen as more robust to use null when clearing the value since it is possible to overwrite undefined, and in that situation assiging undefined would result in unexpected behaviour.