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Javascript Interview Questions and Answers
How to create a popup warning box
alert('Warning: Please enter an integer between 0 and 100.');
How to create a confirmation box?
confirm("Do you really want to launch the missile?");
How to
create an input box?
prompt("What is your temperature?");
How to setting a cookie with the contents of a textbox ?
Values stored in cookies may not have semicolons, commas, or spaces. You
should use the handy "escape()" function to encode the values, and "unescape()"
to retrieve them.
//Sets cookie of current value for myTextBox
function TextBoxOnchange() {
var myBox = window.document.getElementById(myTextBox");
document.cookie = "myTextBox="+ escape(myBox.value) +
getExpirationString();
}
//return a string like ";expires=Thu, 5 Jan 2006 16:07:52 UTC"
function getExpirationString() {
var exp = new Date();
var threemonths = exp.getTime()+(120*24*60*60*1000);
exp.setTime(threemonths);
return ";expires="+exp.toGMTString();
}
This is called from the event handler in the HTML.
<input name="myTextBox" type="text" id="myTextBox"
onchange="javascript:TextBoxOnchange()" />
How to getting values from cookies to set widgets?
function getCookieData(labelName) {
//from Danny Goodman
var labelLen = labelName.length;
// read cookie property only once for speed
var cookieData = document.cookie;
var cLen = cookieData.length;
var i = 0;
var cEnd;
while (i < cLen) {
var j = i + labelLen;
if (cookieData.substring(i,j) == labelName) {
cEnd = cookieData.indexOf(";",j);
if (cEnd == -1) {
cEnd = cookieData.length;
}
return unescape(cookieData.substring(j+1, cEnd));
}
i++;
}
return "";
}
//init() is called from the body tag onload function.
function init() {
setValueFromCookie("brand");
setValueFromCookie("market");
setValueFromCookie("measure");
}
function setValueFromCookie(widget) {
if( getCookieData(widget) != "") {
document.getElementById(widget).value = getCookieData(widget);
}
}
//if you name your cookies the widget ID, you can use the following
helper function
function setCookie(widget) {
document.cookie = widget + "=" +
escape(document.getElementById(widget).value) + getExpirationString();
}
How to change style on an element?
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";
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