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Thus (x === undefined) is not a foolproof way to check whether a variable is undefined, because in versions before ECMAScript 5, it is legal for someone to write var undefined = "I'm defined now";. A more robust approach is to compare using (typeof x === 'undefined'). Functions like this won't work as expected:
In object-oriented programming, the safe navigation operator (also known as optional chaining operator, safe call operator, null-conditional operator, null-propagation operator) is a binary operator that returns null if its first argument is null; otherwise it performs a dereferencing operation as specified by the second argument (typically an ...
A function which never returns has an undefined value because the value can never be observed. Such functions are formally assigned the bottom type, which has no values. Examples fall into two categories: Functions which loop forever. This may arise deliberately, or as a result of a search for something which will never be found.
The return value from a function is provided within the function by making an assignment to an identifier with the same name as the function. [5] However, some versions of Pascal provide a special function Exit(exp); that can be used to return a value immediately from a function, or, without parameters, to return immediately from a procedure. [6]
In object-oriented computer programming, a null object is an object with no referenced value or with defined neutral (null) behavior.The null object design pattern, which describes the uses of such objects and their behavior (or lack thereof), was first published as "Void Value" [1] and later in the Pattern Languages of Program Design book series as "Null Object".
In C and C++ arrays do not support the size function, so programmers often have to declare separate variable to hold the size, and pass it to procedures as a separate parameter. Elements of a newly created array may have undefined values (as in C), or may be defined to have a specific "default" value such as 0 or a null pointer (as in Java).
In other programming languages, Scheme for example, the return value of an assignment is undefined and such idioms are invalid. In Haskell , [ 8 ] there is no variable assignment; but operations similar to assignment (like assigning to a field of an array or a field of a mutable data structure) usually evaluate to the unit type , which is ...
In computer science, a programming language is said to have first-class functions if it treats functions as first-class citizens.This means the language supports passing functions as arguments to other functions, returning them as the values from other functions, and assigning them to variables or storing them in data structures. [1]