How to check ‘undefined’ value in jQuery

JQuery library was developed specifically to simplify and to unify certain JavaScript functionality.

However if you need to check a variable against undefined value, there is no need to invent any special method, since JavaScript has a typeof operator, which is simple, fast and cross-platform:

if (typeof value === "undefined") {
    // ...
}

It returns a string indicating the type of the variable or other unevaluated operand. The main advantage of this method, compared to if (value === undefined) { ... }, is that typeof will never raise an exception in case if variable value does not exist.

Related Posts:

  1. How can I determine if a variable is ‘undefined’ or ‘null’?
  2. How do I redirect to another webpage?
  3. jQuery append() vs appendChild()
  4. ReferenceError: $ is not defined
  5. Cannot read property ‘push’ of undefined when combining arrays
  6. How to deal with net::ERR_SSL_PROTOCOL_ERROR?
  7. jQuery.click() vs onClick
  8. Scroll to an element with jQuery
  9. Download File Using JavaScript/jQuery
  10. Check if checkbox is checked with jQuery
  11. Getting Error “Form submission canceled because the form is not connected”
  12. Is there a link to the “latest” jQuery library on Google APIs?
  13. JavaScript null check
  14. Change Background color (css property) using Jquery
  15. jQuery get textarea text
  16. How can jQuery deferred be used?
  17. Uncaught TypeError : cannot read property ‘replace’ of undefined In Grid
  18. Failed to load resource: net::ERR_FILE_NOT_FOUND loading json.js
  19. Disable/enable an input with jQuery?
  20. Get class name using jQuery
  21. What does on() in JavaScript do?
  22. jQuery animate backgroundColor
  23. Use images like checkboxes
  24. JavaScript error (Uncaught SyntaxError: Unexpected end of input)
  25. ChangeDate – Date Picker Bootstrap
  26. Uncaught TypeError: Cannot read property ‘msie’ of undefined
  27. How to hide a div with jQuery?v
  28. How do I set/unset a cookie with jQuery?
  29. How to convert selected HTML to Json?
  30. How to create a stopwatch using JavaScript?
  31. Failed to load resource: net::ERR_CONTENT_LENGTH_MISMATCH
  32. With jQuery, how do I capitalize the first letter of a text field while the user is still editing that field?
  33. How to update array value javascript?
  34. How to move an element after another element using JS or jquery?
  35. Why is the jquery script not working?
  36. JQuery Datatables : Cannot read property ‘aDataSort’ of undefined
  37. TypeError: $(…).DataTable is not a function
  38. jQuery explode string like PHP
  39. Validate date in dd/mm/yyyy format using JQuery Validate
  40. Javascript/Jquery Convert string to array
  41. Simulate Keypress With jQuery
  42. Adding options to a
  43. Uncaught TypeError: Cannot read property ‘toUpperCase’ of undefined
  44. SyntaxError: JSON.parse: unexpected character at line 1 column 1 of the JSON data
  45. HTML Entity Decode
  46. jQuery remove options from select
  47. jquery beforeunload when closing (not leaving) the page?
  48. How do I pass the this context to a function?
  49. Escaping HTML strings with jQuery
  50. is there something like isset of php in javascript/jQuery?
  51. jQuery – Dynamically Create Button and Attach Event Handler
  52. How to use z-index in svg elements?
  53. What is the best way to detect a mobile device?
  54. How to filter JSON Data in JavaScript or jQuery?
  55. Highlight a word with jQuery
  56. Get querystring from URL using jQuery [duplicate]
  57. jQuery checkbox change and click event
  58. jQuery selectors on custom data attributes using HTML5
  59. How do I refresh a DIV content?
  60. TypeError: abc.getAttribute is not a function
  61. jQuery sort elements using data id
  62. getContext is not a function
  63. How to fire an event on class change using jQuery?
  64. Data column(s) for axis #0 cannot be of type string in google chart dashboard [duplicate]
  65. navigator.geolocation.getCurrentPosition sometimes works sometimes doesn’t
  66. Jquery Value match Regex
  67. Using “&times” word in html changes to ×
  68. How to check if the URL contains a given string?
  69. How should I initialize jQuery?
  70. How to reload page every 5 seconds?
  71. Fire oninput event with jQuery
  72. What is the non-jQuery equivalent of ‘$(document).ready()’?
  73. Changing the selected option of an HTML Select element
  74. How can I unset a JavaScript variable?
  75. How to scroll to top of page with JavaScript/jQuery?
  76. How to set “style=display:none;” using jQuery’s attr method?
  77. Change the selected value of a drop-down list with jQuery
  78. How to dequeue a script?
  79. List of JS Events for Widgets?
  80. JQuery not loading
  81. Uncaught ReferenceError: jQuery is not defined – although jQuery is loaded [closed]
  82. Uncaught TypeError: jQuery(…).slider is not a function
  83. Putting custom html/js page into Elementor as it’s own block
  84. Get the ID of a page in Parent combobox in editor
  85. “jQuery Not Defined” Error When Connecting to PayPal
  86. Fade-in Fade-out doesn’t work in WordPress
  87. Can’t Listen to KeyDown in TInyMCE Iframe (jQuery) and Pass it to Parent HTML FORM
  88. Open image gallery on link click
  89. Uncaught ReferenceError: tippy is not defined
  90. Error – Uncaught TypeError: e.dispatchEvent is not a function

Leave a Comment