JavaScript

1. Java Script Module 2. World Wide Web (WWW) 3. Web Terms 4. NEED FOR SCRIPT 5. Introduction to Internet Programming 6. CLIENT SIDE and SERVER SIDE Scripting 7. Different Scripting Languages 8. Introduction to JavaScript 9. JavaScript and Security 10. How to Enable JavaScript 11. Advantages of Java Script 12. Limitations with JavaScript 13. Difference between JavaScript and JAVA 14. Difference between JavaScript and VBScript 15. JavaScript Development Tools 16. JavaScript Programming Techniques 17. JavaScript terms 18. Starting with JavaScript Programming step by step 19. Time to start JavaScript Programming 20. JavaScript Variables 21. JavaScript RESERVED WORDS 22. JavaScript Data Type 23. NUMBER DATA TYPE 24. BOOLEAN DATA TYPE 25. STRING DATA TYPE 26. NULL DATA TYPE 27. JavaScript Undefined DATA TYPE 28. JavaScript Operators 29. JavaScript Arithmetic Operators 30. JavaScript Logical Operators 31. JavaScript Comparison Operators 32. JavaScript String Operators 33. Bit Manipulation Operators 34. JavaScript Assignment Operators 35. JavaScript Conditional Operator 36. Conversion between JavaScript Data Types 37. Alert JavaScript function 38. confirm JavaScript function 39. prompt JavaScript function 40. JavaScript Statements 41. Single line & Multi-line Comments 42. JavaScrip If Statement 43. JavaScript if..else Statements 44. JavaScript If…else..if statement. 45. JavaScript For Statement 46. JavaScript For..in Statement: 47. JavaScript While Statement 48. JavaScript do while Statement: 49. JavaScript break and continue statement 50. JavaScript switch Statement: 51. JavaScript function() 52. JavaScript function with a Return Value 53. JavaScript with Statement 54. try, catch, and throw Statements 55. JavaScript ARRAY 56. JavaScript array of different data types 57. JavaScript ARRAY and Bubble sorting Program 58. JavaScript Array Methods 59. concate() method 60. every() method 61. filter() method 62. forEach() method 63. indexOf() method 64. Join() method 65. lastIndexOf() method 66. map() method 67. reduce() method 68. reduceRight() method 69. reverse() method 70. some() method 71. toSource() method 72. toString() method 73. pop() method 74. push() method 75. shift () method 76. slice () method 77. splice () method 78. sort() method 79. unshift() method 80. EVENT handling with JavaScript 81. onblur JavaScript Event 82. onchange JavaScript Event 83. onclick JavaScript Event 84. onDblClick JavaScript Event 85. onfocus JavaScript Event 86. onkeydown JavaScript Event 87. onkeyup JavaScript Event 88. Onkeypress JavaScript Event 89. onLoad JavaScript Event 90. onMousedown JavaScript Event 91. onMouseup JavaScript Event 92. Onmouseover JavaScript Event 93. onmouseout JavaScript Event 94. onMouseMove JavaScript Event 95. onReset JavaScript Event 96. onsubmit JavaScript Event 97. onUnload JavaScript Event 98. The Screen Object 99. JavaScript Interview Part1 100. JavaScript Interview Part2 101. JavaScript Interview Part3 102. JavaScript Interview Part4 103. JavaScript Interview Part5 104. JavaScript Interview Part6 105. JavaScript Interview Part7 106. JavaScript Interview Part8 107. JavaScript Interview Part9 108. JavaScript Interview Part10
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JavaScript Undefined DATA TYPE tutorials

  • The undefined value is returned when you use an object property that does not exist, or a variable that has been declared, but has never had a value assigned to it.

  • you can check to see if a variable exists by comparing it to undefined, although you can check if its type is undefined by comparing the type of the variable to the string "undefined". The following example shows how to find out the variable x has been declared:

  • Example: When a variable, for example, is declared without assigning a value to it, it is of undefined type. So

var iAge;

declares a variable called iAge. Its type is undefined; it can be confirmed by simply outputting its type using the typeof operator:

 

Example: The following example shows the use of undefined type.
Output:

iAge is of type: undefined

  • Example: From the following example, the variable carname and model will have the value undefined after the execution of the following statement:

var carname;

var model;

 

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