Javascript Anonymous Functions

4 Key excerpts on "Javascript Anonymous Functions"

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  The JavaScript Workshop

  A New, Interactive Approach to Learning JavaScript

  • Joseph Labrecque, Jahred Love, Daniel Rosenbaum, Nick Turner, Gaurav Mehla, Alonzo L. Hosford, Florian Sloot, Philip Kirkbride(Authors)
  • 2019(Publication Date)
  • Packt Publishing

    (Publisher)

  Objects in the JavaScript language are very tricky. Everything in JavaScript is an object. So, functions in JavaScript are considered functional objects and can be used in the same way as we use objects. Functions in JavaScript can be passed as arguments to other functions as well. Any function that also returns a function is called a function factory. Let's have a look at an example:

  function calculateSum(a, b) {     return () => {         return a + b();     } } let sum = calculateSum(10, () =>20);

  In this example, we have called a function, calculateSum , and passed two parameters to it. One is a number and the other one is a function. This function will return a new function, which will display the passed function followed by the result, as can be seen in the following output:

  Figure 13.8: Examples of anonymous functions

  In the example, you can see we have used a lot of functions without naming them. These functions are very important in JavaScript. A function declared with no particular name is called an anonymous function. We use anonymous functions a lot when programming in JavaScript. These types of functions are declared dynamically at runtime and can be passed as parameters to other functions. For example, Function () {} is a typical example of an anonymous function. You can assign the return value of this function to any variable. Creating functions with this approach allows us to create functions on the go. Anonymous functions are mainly used in callbacks.

  The Differences between Named Functions and Anonymous Functions

  The major difference between named and anonymous functions is that when you declare a named function, the compiler allocates a stored memory block to that function. So, if you have to call it, you can use the name to call it. But with anonymous functions, the memory block is assigned to them and the address is returned, which we can then store in a variable. This helps us initialize functions in places where we can't declare named functions. We can even change the name with which we can call this function by assigning the function to another variable. This can be visualized in the following diagram:

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  eBook - ePub

  Beginning HTML and CSS

  • Rob Larsen(Author)
  • 2013(Publication Date)
  • Wrox

    (Publisher)

  event handler (the code to be run when an event happens) it can be easier to define the function in place without using an identifier.

  Doing so uses the second form you’ve seen, the function expression . A function expression is a function that can be defined more flexibly, as part of a larger piece of JavaScript. For example, you can use a function expression as the value of a variable or as an argument to another function. Commonly function expressions used in this way will be defined without using an identifier. Because it doesn’t have an identifier, this is an anonymous function . A function created in this way works in the same way as a function created with a function declaration. It’s still a collection of JavaScript statements. It differs in that it can be created in place. This code shows an example of an anonymous function assigned to a variable anon :

  var anon = function(){/*code*/}

  This example shows an anonymous function used as an argument to another function, name() :

  name( function(){ return " Rob Larsen " ; });

  It may not make complete sense now, but as you continue to program JavaScript, your ability to create anonymous functions will become more apparent.

  Conditional Statements

  Conditional statements enable you to take different actions depending upon different statements. You will learn about three types of conditional statements:

  • if statements, which are used when you want the script to execute if a condition is true
  • if...else

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  Professional JavaScript for Web Developers

  • Matt Frisbie(Author)
  • 2019(Publication Date)
  • Wrox

    (Publisher)

  Chapter 4 ). Storing a scope in which an HTML element is stored effectively ensures that the element cannot be destroyed. Consider the following:

  function assignHandler() { let element = document.getElementById('someElement'); element.onclick = () => console.log(element.id); }

  This code creates a closure as an event handler on element , which in turn creates a circular reference (events are discussed in Chapter 13 ). The anonymous function keeps a reference to the assignHandler() function's activation object, which prevents the reference count for element from being decremented. As long as the anonymous function exists, the reference count for element will be at least 1, which means the memory will never be reclaimed. This situation can be remedied by changing the code slightly, as shown here:

  function assignHandler() { let element = document.getElementById('someElement');

  let id = element.id;

  element.onclick = () => console.log(id);

  element = null;

  }

  In this version of the code, a copy of element 's ID is stored in a variable that is used in the closure, eliminating the circular reference. That step alone is not enough, however, to prevent the memory problem. Remember that the closure has a reference to the containing function's entire activation object, which contains element . Even if the closure doesn't reference element directly, a reference is still stored in the containing function's activation object. It is necessary, therefore, to set the element variable equal to null . This dereferences the COM object and decrements its reference count, ensuring that the memory can be reclaimed when appropriate.

  IMMEDIATELY INVOKED FUNCTION EXPRESSIONS

  An anonymous function that is called immediately is most often called an immediately invoked function expression (IIFE)

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  eBook - ePub

  JavaScript: Novice to Ninja

  • Darren Jones(Author)
  • 2017(Publication Date)
  • SitePoint

    (Publisher)

  Chapter 4: Functions

  A function is a chunk of code that can be referenced by a name, and is almost like a small, self-contained mini program. Functions can help reduce repetition and make code easier to follow. In this chapter, we’ll be covering these topics:

  • Defining functions―function declarations, function expressions, Function() constructors and the new arrow syntax
  • Invoking a function
  • Return values
  • Parameters and arguments
  • Hoisting―variables and functions
  • Callbacks―functions as a parameter
  • Project ― we’ll be using functions to make the Quiz Ninja code easier to follow

  In JavaScript, functions are considered to be first-class objects. This means they behave in the same way as all the other primitive data types and objects in the language. They can be be assigned to variables, stored in arrays and can even be returned by another functions.

  This makes functions a very important and powerful part of the JavaScript language with many of its features relying on them. Fully understanding functions is an essential skill of the JavaScript ninja.

  Defining a Function

  There are a number of ways to define a function in JavaScript. Three of the most common are covered below. ES6 introduced a new way to define functions, using what is known as 'arrow' notation. This is covered later in the chapter.

  Function Declarations

  To define a function literal we can use a function declaration:

  function hello(){ console.log('Hello World!'); }

  This starts with the function keyword and is followed by the name of the function, which in this case is called 'hello ', followed by parentheses. Following this is a block that contains the code for the function.

  This is known as a named function as the function has a name: 'hello '.

  Function Expressions

  Another way of defining a function literal is to create a function expression. This assigns an anonymous function

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