51. What is the difference between undefined value and null value?
Undefined value: A value that is not defined and has no keyword is known as undefined value. For example:
var number;//Here, number has undefined value.
Null value: A value that is explicitly specified by the keyword “null” is known as null value. For example:
var str=null;//Here, str has a null value.
52. How to submit a form using JavaScript by clicking a link?
Let’s see the JavaScript code to submit form on clicking the link.
<form name=”myform” action=”index.php”>
Search: <input type=’text’ name=’query’ />
<a href=”javascript: submitform()”>Search</a>
</form>
<script type=”text/javascript”>
function submitform()
{
document.myform.submit();
}
</script>
53. How to change the background color of HTML document using JavaScript?
<script type=”text/javascript”>
document.body.bgColor=”pink”;
</script>
54. How can you read properties of an Object in JavaScript?
You can write and read properties of an object using the dot notation as follows −
Getting object properties
emp.name // ==> Zara
emp.age // ==> 10
Setting object properties
emp.name = “Daisy” // <== Daisy
emp.age = 20 // <== 20
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55. How can you create an Array in JavaScript?
You can define arrays using the array literal as follows −
var x = [];
var y = [1, 2, 3, 4, 5];
56. How to read elements of an array in JavaScript?
An array has a length property that is useful for iteration. We can read elements of an array as follows −
var x = [1, 2, 3, 4, 5];
for (var i = 0; i < x.length; i++) {
// Do something with x[i]
}
57. What is a named function in JavaScript? How to define a named function?
A named function has a name when it is defined. A named function can be defined using function keyword as follows −
function named(){
// do some stuff here
}
58. How to define a anonymous function?
An anonymous function can be defined in similar way as a normal function but it would not have any name.
59. Can you assign a anonymous function to a variable?
Yes! An anonymous function can be assigned to a variable.
60. What is the purpose of ‘this’ operator in JavaScript?
JavaScript famous keyword this always refers to the current context.
