Referencing a JavaScript value before it is declared – can someone explain this

by

Function declarations are subject of hoisting, and they are evaluated at parse time, by hoisting means that they are available to the entire scope in where they were declared, for example:

foo(); // alerts foo
foo = function () { alert('bar')};
function foo () { alert('foo');}
foo(); // alerts bar

The first call to foo will execute the function declaration, because at parse time it was made available, the second call of foo will execute the function expression, declared at run-time.

For a more detailed discussion about the differences between function expressions and function declarations, check this question and this article.

More Related Contents:

  1. Attaching Dynamic Variable in ES6 [closed]
  2. Javascript won’t output values from input box
  3. When I load the page the alert(“hey”) function appears, why does the js function execute despite no onClick call? How do I prevent it from doing so?
  4. What is lexical scope?
  5. using brackets with javascript import syntax
  6. ES6 variable import name in node.js?
  7. Finding matches between multiple JavaScript Arrays
  8. JavaScript “cannot read property “bar” of undefined [duplicate]
  9. Breakpoint on property change
  10. React Hooks useState() with Object
  11. Select all contents of textbox when it receives focus (Vanilla JS or jQuery)
  12. In jQuery, how do I select an element by its name attribute?
  13. How can I update window.location.hash without jumping the document?
  14. Get value of input field inside an iframe
  15. How do I mock a service that returns promise in AngularJS Jasmine unit test?
  16. Why React Hook useState uses const and not let
  17. How can I use modulo operator (%) in JavaScript? [duplicate]
  18. How to convert hex string into a bytes array, and a bytes array in the hex string?
  19. Get the weekday from a Date object or date string using JavaScript
  20. “RangeError: Maximum call stack size exceeded” Why?
  21. How do you make javascript code execute *in order*
  22. Why does (“foo” === new String(“foo”)) evaluate to false in JavaScript?
  23. Inheriting from the Error object – where is the message property?
  24. How to use JavaScript to change the form action [duplicate]
  25. Iteration ng-repeat only X times in AngularJs
  26. window.opener alternatives
  27. visibilitychange event is not triggered when switching program/window with ALT+TAB or clicking in taskbar
  28. C# MVC Controller cannot get decimal or double values from Ajax POST request
  29. Is there an “after submit” jQuery option?
  30. jQuery SVG vs. Raphael [closed]

Leave a Comment