JAVASCRIPT interview questions part-IV

54. What is a prompt box?
Ans. A prompt box allows the user to enter input by providing a text box.

55. Can javascript code be broken in different lines?
Ans. Breaking is possible within a string statement by using a backslash \ at the end but not within any other javascript statement.
that is ,

document.write("Hello \ world");

is possible but not

document.write \ ("hello world");

56. How you put a “close window” link on a page ?
Ans.

<a class="mainnav" href="javascript:window.close()"> Close </a>

57. How to hide javascript code from old browsers that dont run it?
Ans.Use the below specified style of comments

// <![CDATA[ javascript code goes here // ]]>

or Use the

<noscript>some html code</noscript>

tags and code the display html statements between these and this will appear on the page if the browser does not support javascript.

58. Name the numeric constants representing max,min values.
Ans.

Number.MAX_VALUE Number.MIN_VALUE

59. How to write messages to the screen without using “document.write()” ?
Ans. Changing the contents of an element is a much better solution. When the method showStatus is invoked it will change the content of the span.

function showStatus(message) { var element = document.getElementById("mystatus"); element.textContent = message; //for Firefox element.innerHTML = message; //for IE (why can't we all just get along?) return true; }

<span id="mystatus">Test. </span>

60. How to change style on an element?
Ans. Between CSS and javascript is a weird symmetry. CSS style rules are layed on top of the DOM. The CSS property names like “font-weight” are transliterated into “myElement.style.fontWeight”. The class of an element can be swapped out. For example:

document.getElementById("myText").style.color = "green"; document.getElementById("myText").style.fontSize = "20"; //or document.getElementById("myText").className = "regular";

61. How to remove the event listener: ?
Ans.

document.getElementById("hitme4").removeEventListener("click", hitme4, false);

62. How to make elements invisible ?
Ans. Change the “visibility” attribute of the style object associated with your element. Remember that a hidden element still takes up space, use “display” to make the space disappear as well.

if ( x == y) { myElement.style.visibility = 'visible'; } else { myElement.style.visibility = 'hidden'; }

63. How to set the cursor to wait ?
Ans. In theory, we should cache the current state of the cursor and then put it back to its original state.

document.body.style.cursor = 'wait'; //do something interesting and time consuming document.body.style.cursor = 'auto';

64. How to reload the current page ?
Ans.

window.location.reload(true);

65. how to force a page to go to another page using JavaScript ?
Ans.

location.href=http://www.google.com;

66. How to create a function using function constructor?
Ans. The following example creates a function called square with argument x and returns x multiplied by itself.

var square = new Function ("x","return x*x");

67. Have you heard of Douglas Crockford?
Ans. Yes he is the “inventor” of JSON.

68. What debugging tools do you use?
Ans. Firebug in Firefox (console.log(); method) and Visual Studio in IE (‘debug’ command inserted in javascript file).