JavaScript hoisting is basically that declarations are moved to the top of your code.
Actually your function and variable declarations are added to memory during the compile phase.
And they stay exactly where you typed them in your code.
JavaScript hoists all declarations
JavaScript hoists all declarations. Initializations are not hoisted.
Declare and initialize a variable, e.g. var x = 8;, only the var x; part (the declaration) is hoisted.
The x = 8; (the initialization) is not hoisted.
A variable that is declared but not initialized is automatically set as undefined.
Take a look at the examples to understand this.
Hoisting Variables Examples
// This is how you would expect to write the code var x = 8; // Initialize and assign 8 to x console.log('X has the value: '+ x); // The printed text is: "X has the value: 8" // Here y is assigned before it is declared y = 8; // Assign 8 to y console.log('Y has the value: '+ y); // The printed text is: "Y has the value: 8" var y; // Declare y
Hoisting Variables Undefined Examples
// Declare and assign the variable at the end // Only the declaration is hoisted console.log('Z has the value: '+ z); // The printed text is: "Z has the value: undefined" var z = 8; // Declare and assign 8 to z
Hoisting Functions Examples
// This is how you would expect to write the code function printName(name) { console.log("My name is " + name); } printName("Donald"); // The printed text is: "My name is Donald" // Here the function is called before it is declared printCity("London"); // The printed text is: "My favorite city is London" function printCity(name) { console.log("My favorite city is " + name); }
Let and Const Statement
Variables and constants declared with let or const are not hoisted!
Hoisting Best Practices
Hoisting is not well known to many developers.
It is considered a best practice to declare variables at the top of their respective scopes. Then you would limit undesirable effects.
Always initialize variables when they are declared. This will provide better code and avoid undefined variables.
JavaScript strict mode gives an error if variables is used before they are declared.
Scope determines if variables are accessible (visible).
A scope in JavaScript defines what variables you have access to. There are two kinds of scope – global scope and local scope.
Function scope and block scope are local scope - variables declared inside a function or a bl....
Const is a keyword that indicates a constant. It describes an entity that cannot be changed at runtime. We cannot reassign a constant. With constants we lose the ability to modify variables at runtime and we gain run-time validation.
One of t....
There will be errors in the code. It is good practice to handle exceptions/errors.
Exceptions are a type of error that occurs during the execution of an application. Errors should be logged. Sometimes it is possible to recover a bug and proceed.
Other cases the user should get inform....
JavaScript comments can be used to to explain and make the code more readable. JavaScript comments can also prevent execution of code.
It is possible to comment code as a single-line comment or as a multi-line comment.
JavaScript is one of the 3 core language technologies of the World Wide Web that all web developers must learn:
1. HTML to define the content of web pages.
2. CSS to specify the layout of web pages.
3. JavaScript to program the behavior of web pages.
JavaScript is a scripting or programming language that allows you to implement complex things on web pages. Every time a web page does more than just sit there and display static information for you to look at, displaying timely content updates, interactive maps, animated 2D/3D graphics, scrolling video jukeboxes, etc. − you can bet that JavaScript is probably involved. The benefits of using JavaScript are: 1. You can validate user input before sending the page off to the server. This saves server traffic, which means less load on your server. 2. Immediate feedback to the visitors − They don't have to wait for a page reload to see if they have forgotten to enter something. 3. Increased interactivity − You can create interfaces that react when the user hovers over them with a mouse or activates them via the keyboard. 4. Richer interfaces − You can use JavaScript to include such items as drag-and-drop components and sliders to give a Rich Interface to your site visitors.
The NDC Conferences (Norwegian Developers Conference) are one of the world`s largest independent software conferences for .NET & Agile development. The conference covers everything you need to know within software development. The conferences are held each year in many places such as Oslo, Copenhagen, London, Sydney and Minnesota.
Update Conference Prague is the biggest developer conference in the Czech Republic. The conference is offering sessions delivered by the top experts from all around the world. Their goal is to inspire the attendees and enrich their knowledge.
Learn about Web Security from Troy Hunt. He is a really engaged speaker that frequently give talks on conferences around the world. Troy is a Microsoft MVP and you can even learn from him on some great courses on Pluralsight.
W3Schools.com is a great education Web Site for learning web technologies. On W3Schools you may find well organized basic to advanced tutorials and references.
Learn about Web Technologies and new trends from Scott Hanselman. Scott Hanselman is an author of developer books and he is an engaged speaker that usually talks about the Microsoft stack. You may meet Scott on conferences around the world.
DeveloperWeek is one of the world’s largest developer conferences. Developer Week focus on new dev technologies, the conference have talks and workshops for newbies and experienced audience. You can attend on a Developer Week conference different places in Nothern America.