nested function

What are nested functions?

Nested functions in programming refer to a function that is defined inside another function. These functions can access the variables that are present in the enclosing function.


function outerFunction(x) {
  function innerFunction(y) {
    return x + y;
  return innerFunction;

var addTwo = outerFunction(2);
var result = addTwo(4); // returns 6

In the above example, the outerFunction returns a reference to the innerFunction. The addTwo variable is assigned the reference to the returned innerFunction. When addTwo is called with an argument of 4, it returns the sum of the argument and the variable x which is set to 2.

Benefits of nested functions:

  • Encapsulation: Nested functions can be used to encapsulate functionality within a larger function, making the code more organized and easier to read.
  • Closure: Nested functions have access to the variables of the enclosing function, which can be useful in creating closures.
  • Reduced namespace pollution: By defining functions within other functions, the number of global variables can be reduced, which helps prevent naming conflicts.

Additional ways to create nested functions:

In addition to defining a nested function within another function, there are other ways to create nested functions in various programming languages:

  • In Python, nested functions can be created using the def keyword within another function.
  • In Ruby, nested functions can be created using the def keyword within another function or block.
  • In PHP, nested functions can be created using the function keyword within another function.

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