What does double underscore __ in front of a variable means in node JS?

Double underscore (__) in front of a variable is a convention. It is used for global variable (The following variables may appear to be global but are not, rather local to each module) in Nodejs meanwhile Underscore(_) used to define private variable.

How do you declare a variable in JavaScript?

Creating a variable in JavaScript is called “declaring” a variable. You declare a JavaScript variable with the var keyword: var carName; After the declaration, the variable has no value (technically it has the value of undefined ).

How functions are declared in JavaScript?

The function statement declares a function. A declared function is “saved for later use”, and will be executed later, when it is invoked (called). In JavaScript, functions are objects, and they have both properties and methods. A function can also be defined using an expression (See Function Definitions).

Why is function declaration placed prior to function definition?

The reason modern compilers give warnings on an attempt to call a function before seeing a declaration is that a declaration allows the compiler to check if arguments are of the expected type.

What is the purpose of __ filename variable?

The __filename represents the filename of the code being executed. This is the resolved absolute path of this code file. For a main program, this is not necessarily the same filename used in the command line.

What does double underscore mean in Python?

Double underscores are used for fully private variables. According to Python documentation − If your class is intended to be subclassed, and you have attributes that you do not want subclasses to use, consider naming them with double leading underscores and no trailing underscores.

What are the two ways of declaring a variable?

Basically we can declare variables in three different ways by using var, let and const keyword. Each keyword is used in some specific conditions. var: This keyword is used to declare variable globally. If you used this keyword to declare variable then the variable can accessible globally and changeable also.

How is function declared?

You can declare a function by providing its return value, name, and the types for its arguments. The names of the arguments are optional. A function definition counts as a function declaration.

What is function how functions are declared?

A function is a group of statements that together perform a task. A function declaration tells the compiler about a function’s name, return type, and parameters. A function definition provides the actual body of the function. The C++ standard library provides numerous built-in functions that your program can call.

Is it necessary to declare function before use?

It is always recommended to declare a function before its use so that we don’t see any surprises when the program is run (See this for more details).

Why function declaration is important?

Function declarations are important because a calling convention (part of the ABI of a platform) can define different places for arguments and return values based on the types a function returns and accepts as arguments.