What are undefined and undeclared variables?

Q

✍: Guest

A

Undeclared variables are those that are not declared in the program (do not exist at all), trying to read their values gives runtime error. But if undeclared variables are assigned then implicit declaration is done .

Undefined variables are those that are not assigned any value but are declared in the program. Trying to read such variables gives special value called undefined value.

2008-12-02, 4739👍, 0💬

What does undefined value mean in JavaScript?
What does undefined value mean in JavaScript? Undefined value means the variable used in the code doesn't exist or is not assigned any value, or the property doesnt exist. 2008-11-18, 5271👍, 0💬

What is variable typing in JavaScript?
What is variable typing in JavaScript? It is perfectly legal to assign a number to a variable and then assign a string to the same variable as in the following example: i = 10; i = "string"; This is called variable typing 2008-11-25, 4982👍, 0💬

How to select an element by id and swapping an image?
How to select an element by id and swapping an image? ... <script language="JavaScript" type="text/javascript" > function setBeerIcon() { var beerIcon = document.getElementById("beerI con");beerIcon.src = "images/"+getSelectValue("beer ")+".jpg";} </script> ... <img border="0" s... 2008-11-18, 4974👍, 0💬

What are undefined and undeclared variables?
What are undefined and undeclared variables? Undeclared variables are those that are not declared in the program (do not exist at all), trying to read their values gives runtime error. But if undeclared variables are assigned then implicit declaration is done . Undefined variables are those that are... 2008-12-02, 4740👍, 0💬

What is === operator?
What is === operator? ==== is strict equality operator, it returns true only when the two operands are having the same value without any type conversion. 2008-12-09, 4715👍, 0💬

What is the difference between undefined value and null value?
What is the difference between undefined value and null value? Undefined value cannot be explicitly stated that is there is no keyword called undefined whereas null value has keyword called null. typeof undefined variable or property returns undefined whereas typeof null value returns object 2008-11-25, 4692👍, 0💬

How to find radio button selection when a form is submitted?
How to find radio button selection when a form is submitted? <script type="text/javascript"> function findButton() { var myForm = document.forms.animalForm; var i; for (i=0;i<myForm.marsupial .length;i++) { if (myForm.marsupial[i].checked) { break; } } alert("You selected \""+myForm.ma... 2008-12-16, 4633👍, 0💬

How to find the selected radio button immediately using the this variable?
How to find the selected radio button immediately using the 'this' variable? <script> function favAnimal(button) { alert('You like '+button.value+'s.'); } </script> <input type="radio" name="marsupial" value="kangaroo" onchange="favAnimal(this)">Kan garoo<br /><inp... 2008-12-09, 4604👍, 0💬

Does JavaScript have the concept level scope?
Does JavaScript have the concept level scope? No. JavaScript does not have block level scope, all the variables declared inside a function possess the same level of scope unlike c, c++, and java. 2008-12-02, 4588👍, 0💬

All rights in the contents of this web site are reserved by the individual author. fyicenter.com does not guarantee the truthfulness, accuracy, or reliability of any contents.