variable === undefined vs. typeof variable === “undefined”

by

For undeclared variables, typeof foo will return the string literal "undefined", whereas the identity check foo === undefined would trigger the error “foo is not defined”.

For local variables (which you know are declared somewhere), no such error would occur, hence the identity check.

More Related Contents:

  1. How can I determine if a variable is ‘undefined’ or ‘null’?
  2. Disable/enable an input with jQuery?
  3. $(document).ready equivalent without jQuery
  4. Event detect when css property changed using Jquery
  5. document.getElementById vs jQuery $()
  6. Load jQuery with Javascript and use jQuery
  7. preventDefault() on an tag
  8. Stop a youtube video with jquery?
  9. Determine if an element has a CSS class with jQuery
  10. Scroll smoothly to specific element on page
  11. Background-color hex to JavaScript variable
  12. How to pass javascript object from one page to other
  13. syntax error: unexpected token
  14. How to check browser for touchstart support using JS/jQuery?
  15. Selecting multiple from an html select element without using ctrl key
  16. jquery ajax readystate 0 responsetext status 0 statustext error
  17. Anchor tag download attribute not working :Bug in Chrome 35.0.1916.114
  18. How to check if an element is in the view of the user with jquery
  19. CSS fade left to right
  20. jQuery – Create hidden form element on the fly
  21. jQuery: checking if the value of a field is null (empty)
  22. Preloading images in HTML
  23. Get the content (text) of an URL after Javascript has run with PHP
  24. IE10/11 Ajax XHR error – SCRIPT7002: XMLHttpRequest: Network Error 0x2ef3
  25. Bind events on dynamic created elements inserted by AJAX (check box)
  26. How do you handle a form change in jQuery?
  27. lodash debounce not working in anonymous function
  28. Cancel click event in the mouseup event handler
  29. Javascript: Easier way to format numbers? [closed]
  30. How to replace the entire html webpage with ajax response?

Leave a Comment