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Javascript array length through user input

I have a problem in Javascript I want to make a form which have one input text field and one button when I click on the button window.prompt is called.
It will prompt depend upon my array length but I want array length get through input text field when I write 10 it will prompt 10 times when I write 2 it will prompt 2 times.
How can i write this type of query?
I tried this code but its not working.
words = new Array (4);
function a() {
for ( k = 0 ; k < words.length ; k = k + 1 ) {
words[ k ] = window.prompt( "Enter word # " + k, "" ) ;
}
}

Maybe you forgot to call your function a().
Some remarks about your code:
You don't have to specify an initial array size, e.g. words = [] or words = new Array() is enough.
Also k=k+1 is usually written as k++.
A remark about asking questions:
Use punctuation to make sentences! Your whole question is one sentence.

Hopefully it's just the snippet of code but I hope you are using var somewhere to declare all those variables.
Otherwise this should do the trick, however not sure what you are trying to achieve but this sounds like a bad user experience.
Here is the jsffidle http://jsfiddle.net/R2bCz/1/
function Handler(event) {
var count = event.target.value;
var i = 0;
var words = [];
var word;
for (; i < count; i++) {
word = window.prompt("Enter word # " + i, "");
words.push(word);
}
}
$("#multi").on("change", Handler);

Javascript splitting by commas

i am relatively new to stackoverflow and have searched for some time for an answer to my question. I found some links like this one How to split a comma-separated string?
but still can't quite understand what I am doing wrong with my short little javascript program.
Anyway here it is. Help would be appreciated.
I basically am trying to create a prompt that asks the user to input 3 numbers seperated by commas, then change that string into an array so that I can multiply the values later on. So far, when i try to console.log this my results are as follows : 1,2
It doesn't print out the third digit(3rd number entered by the user).
var entry = prompt("Triangle side lengths in cm (number,number,number):")
if(entry!=null && entry!="") {
entryArray = entry.split(",");
for (i=0; i<3; i++)
{
entryArray[i] = entry.charAt([i]);
}
}
console.log(entryArray[0] + entryArray[1] + entryArray[2]);

Split creates an array already. So, if you enter 1,2,3, you get an array like this when you split it: ["1", "2", "3"]. In your for loop, you are getting the characters from the original input, not your array. In order to add them, you need to change the input to numbers since they are considered strings. So your for loop should look like this:
for (i=0; i<3; i++)
{
entryArray[i] = parseFloat(entryArray[i]);
}
overwriting the strings with the digits.

Try
for (i=0; i<3; i++)
{
entryArray.push(parseInt(entryArray[i]);
}

You can remove the body of the for。like this:
var entry = prompt("Triangle side lengths in cm (number,number,number):")
console.log(entry);
if(entry!=null && entry!="") {
entryArray = entry.split(",");
console.log(entryArray);
}
console.log(entryArray[0] + entryArray[1] + entryArray[2]);

try this code, i removed your looping which was overwriting the array.
var entry = prompt("Triangle side lengths in cm (number,number,number):");
if(entry!=null && entry!="") {
entryArray = entry.split(",");
console.log(entryArray[0] + entryArray[1] + entryArray[2]);
}

Searching for most performant way for string replacing with javascript

I'm programming my own autocomplete textbox control using C# and javascript on clientside. On client side i want to replace the characters in string which matching the characters the user was searching for to highlight it. For example if the user was searching for the characters 'bue' i want to replace this letters in the word 'marbuel' like so:
mar<span style="color:#81BEF7;font-weight:bold">bue</span>l
in order to give the matching part another color. This works pretty fine if i have 100-200 items in my autocomplete, but when it comes to 500 or more, it takes too mutch time.
The following code shows my method which does the logic for this:
HighlightTextPart: function (text, part) {
var currentPartIndex = 0;
var partLength = part.length;
var finalString = '';
var highlightPart = '';
var bFoundPart = false;
var bFoundPartHandled = false;
var charToAdd;
for (var i = 0; i < text.length; i++) {
var myChar = text[i];
charToAdd = null;
if (!bFoundPart) {
var myCharLower = myChar.toLowerCase();
var charToCompare = part[currentPartIndex].toLowerCase();
if (charToCompare == myCharLower) {
highlightPart += myChar;
if (currentPartIndex == partLength - 1)
bFoundPart = true;
currentPartIndex++;
}
else {
currentPartIndex = 0;
highlightPart = '';
charToAdd = myChar;
}
}
else
charToAdd = myChar;
if (bFoundPart && !bFoundPartHandled) {
finalString += '<span style="color:#81BEF7;font-weight:bold">' + highlightPart + '</span>';
bFoundPartHandled = true;
}
if (charToAdd != null)
finalString += charToAdd;
}
return finalString;
},
This method only highlight the first occurence of the matching part.
I use it as follows. Once the request is coming back from server i build an html UL list with the matching items by looping over each item and in each loop i call this method in order to highlight the matching part.
As i told for up to 100 items it woks pretty nice but it is too mutch for 500 or more.
Is there any way to make it faster? Maybe by using regex or some other technique?
I also thought about using "setTimeOut" to do it in a extra function or maybe do it only for the items, which currently are visible, because only a couple of items are visible while for the others you have to scroll.

Try limiting visible list size, so you are only showing 100 items at maximum for example. From a usability standpoint, perhaps even go down to only 20 items, so it would be even faster than that. Also consider using classes - see if it improves performance. So instead of
mar<span style="color:#81BEF7;font-weight:bold">bue</span>l
You will have this:
mar<span class="highlight">bue</span>l

String replacement in JavaScript is pretty easy with String.replace():
function linkify(s, part)
{
return s.replace(part, function(m) {
return '<span style="color:#81BEF7;font-weight:bold">' + htmlspecialchars(m) + '</span>';
});
}
function htmlspecialchars(txt)
{
return txt.replace('<', '<')
.replace('>', '>')
.replace('"', '"')
.replace('&', '&');
}
console.log(linkify('marbuel', 'bue'));

I fixed this problem by using regex instead of my method posted previous. I replace the string now with the following code:
return text.replace(new RegExp('(' + part + ')', 'gi'), "<span>$1</span>");
This is pretty fast. Much faster as the code above. 500 items in the autocomplete seems to be no problem. But can anybody explain, why this is so mutch faster as my method or doing it with string.replace without regex? I have no idea.
Thx!

Javascript for Variations with Repetition (combinatorics) of missing string characters

My question is similar to THIS question that hasn't been answered yet.
How can I make my code (or any javascript code that might be suggested?) find all possible solutions of a known string length with multiple missing characters in variation with repetition?
I'm trying to take a string of known character lengths and find missing characters from that string. For example:
var missing_string = "ov!rf!ow"; //where "!" are the missing characters
I'm hoping to run a script with a specific array such as:
var r = new Array("A","B","C","D","E","F","G","H","I","J","K",
"L","M","N","O","P","Q","R","S","T","U","V",
"W","X","Y","Z",0,1,2,3,4,5,6,7,8,9);
To find all the possible variations with repetition of those missing characters to get a result of:
ovArfAow
ovBrfAow
ovCrfAow
...
ovBrfBow
ovBrfCow
...
etc //ignore the case insensitive, just to emphasize the example
and of course, eventually find ovErfLow within all the variations with repetition.
I've been able to make it work with 1 (single) missing character. However, when I put 2 missing characters with my code it obviously repeats the same array character for both missing characters which is GREAT for repition but I also need to find without repetition as well and might need to have 3-4 missing characters as well which may or may not be repeated. Here's what I have so far:
var r = new Array("A","B","C","D","E","F","G","H","I","J","K",
"L","M","N","O","P","Q","R","S","T","U","V",
"W","X","Y","Z",0,1,2,3,4,5,6,7,8,9);
var missing_string = "he!!ow!r!d";
var bt_lng = missing_string.length;
var bruted="";
for (z=0; z<r.length; z++) {
for(var x=0;x<bt_lng;x++){
for(var y=0;y<r.length;y++){
if(missing_string.charAt(x) == "!"){
bruted += r[z];
break;
}
else if(missing_string.charAt(x) == r[y]){
bruted += r[y];
}
}
}
console.log("br: " + bruted);
bruted="";
}
This works GREAT with just ONE "!":
helloworAd
helloworBd
helloworCd
...
helloworLd
However with 2 or more "!", I get:
heAAowArAd
heBBowBrBd
heCCowCrCd
...
heLLowLrLd
which is good for the repetition part but I also need to test all possible array M characters in each missing character spot.

Maybe the following function in pure javascript is a possible solution for you. It uses Array.prototype.reduce to create the cartesian product c of the given alphabet x, whereby its power n depends on the count of the exclamation marks in your word w.
function combinations(w) {
var x = new Array(
"A","B","C","D","E","F","G","H","I","J","K",
"L","M","N","O","P","Q","R","S","T","U","V",
"W","X","Y","Z",0,1,2,3,4,5,6,7,8,9
),
n = w.match(/\!/g).length,
x_n = new Array(),
r = new Array(),
c = null;
for (var i = n; i > 0; i--) {
x_n.push(x);
}
c = x_n.reduce(function(a, b) {
var c = [];
a.forEach(function(a) {
b.forEach(function(b) {
c.push(a.concat([b]));
});
});
return c;
}, [[]]);
for (var i = 0, j = 0; i < c.length; i++, j = 0) {
r.push(w.replace(/\!/g, function(s, k) {
return c[i][j++];
}));
}
return r;
}
Call it like this console.log(combinations("ov!rf!ow")) in your browser console.

Fastest way to search string in javascript

I have a hidden field on my page that stores space separated list of emails.
I can have maximum 500 emails in that field.
What will be the fastest way to search if a given email already exists in that list?
I need to search multiple emails in a loop
use RegEx to find a match
use indexOf()
convert the list to a
javascript dictionary and then
search
If this is an exact duplicate, please let me know the other question.
Thanks
EDIT:
Thanks everyone for your valuable comments and answers.
Basically my user has a list of emails(0-500) in db.
User is presented with his own contact list.
User can then choose one\more emails from his contact list to add to the list.
I want to ensure at client side that he is not adding duplicate emails.
Whole operation is driven by ajax, so jsvascript is required.

The answer is: It depends.
It depends on what you actually want to measure.
It depends on the relationship between how many you're searching for vs. how many you're searching.
It depends on the JavaScript implementation. Different implementations usually have radically different performance characteristics. This is one of the many reasons why the rule "Don't optimize prematurely" applies especially to cross-implementation JavaScript.
...but provided you're looking for a lot fewer than you have in total, it's probably String#indexOf unless you can create the dictionary once and reuse it (not just this one loop of looking for X entries, but every loop looking for X entries, which I tend to doubt is your use-case), in which case that's hands-down faster to build the 500-key dictionary and use that.
I put together a test case on jsperf comparing the results of looking for five strings buried in a string containing 500 space-delimited, unique entries. Note that that jsperf page compares some apples and oranges (cases where we can ignore setup and what kind of setup we're ignoring), but jsperf was being a pain about splitting it and I decided to leave that as an exercise for the reader.
In my tests of what I actually think you're doing, Chrome, Firefox, IE6, IE7 and IE9 did String#indexOf fastest. Opera did RegExp alternation fastest. (Note that IE6 and IE7 don't have Array#indexOf; the others do.) If you can ignore dictionary setup time, then using a dictionary is the hands-down winner.
Here's the prep code:
// ==== Main Setup
var toFind = ["aaaaa100#zzzzz", "aaaaa200#zzzzz", "aaaaa300#zzzzz", "aaaaa400#zzzzz", "aaaaa500#zzzzz"];
var theString = (function() {
var m, n;
m = [];
for (n = 1; n <= 500; ++n) {
m.push("aaaaa" + n + "#zzzzz");
}
return m.join(" ");
})();
// ==== String#indexOf (and RegExp) setup for when we can ignore setup
var preppedString = " " + theString + " ";
// ==== RegExp setup for test case ignoring RegExp setup time
var theRegExp = new RegExp(" (?:" + toFind.join("|") + ") ", "g");
// ==== Dictionary setup for test case ignoring Dictionary setup time
var theDictionary = (function() {
var dict = {};
var index;
var values = theString.split(" ");
for (index = 0; index < values.length; ++index) {
dict[values[index]] = true;
}
return dict;
})();
// ==== Array setup time for test cases where we ignore array setup time
var theArray = theString.split(" ");
The String#indexOf test:
var index;
for (index = 0; index < toFind.length; ++index) {
if (theString.indexOf(toFind[index]) < 0) {
throw "Error";
}
}
The String#indexOf (ignore setup) test, in which we ignore the (small) overhead of putting spaces at either end of the big string:
var index;
for (index = 0; index < toFind.length; ++index) {
if (preppedString.indexOf(toFind[index]) < 0) {
throw "Error";
}
}
The RegExp alternation test:
// Note: In real life, you'd have to escape the values from toFind
// to make sure they didn't have special regexp chars in them
var regexp = new RegExp(" (?:" + toFind.join("|") + ") ", "g");
var match, counter = 0;
var str = " " + theString + " ";
for (match = regexp.exec(str); match; match = regexp.exec(str)) {
++counter;
}
if (counter != 5) {
throw "Error";
}
The RegExp alternation (ignore setup) test, where we ignore the time it takes to set up the RegExp object and putting spaces at either end of the big string (I don't think this applies to your situation, the addresses you're looking for would be static):
var match, counter = 0;
for (match = theRegExp.exec(preppedString); match; match = theRegExp.exec(preppedString)) {
++counter;
}
if (counter != 5) {
throw "Error";
}
The Dictionary test:
var dict = {};
var index;
var values = theString.split(" ");
for (index = 0; index < values.length; ++index) {
dict[values[index]] = true;
}
for (index = 0; index < toFind.length; ++index) {
if (!(toFind[index] in dict)) {
throw "Error";
}
}
The Dictionary (ignore setup) test, where we don't worry about the setup time for the dictionary; note that this is different than the RegExp alternation (ignore setup) test because it assumes the overall list is invariant:
var index;
for (index = 0; index < toFind.length; ++index) {
if (!(toFind[index] in theDictionary)) {
throw "Error";
}
}
The Array#indexOf test (note that some very old implementations of JavaScript may not have Array#indexOf):
var values = theString.split(" ");
var index;
for (index = 0; index < toFind.length; ++index) {
if (values.indexOf(toFind[index]) < 0) {
throw "Error";
}
}
The Array#indexOf (ignore setup) test, which like Dictionary (ignore setup) assumes the overall list is invariant:
var index;
for (index = 0; index < toFind.length; ++index) {
if (theArray.indexOf(toFind[index]) < 0) {
throw "Error";
}
}

Instead of looking for the fastest solution, you first need to make sure that you’re actually having a correct solution. Because there are four cases an e-mail address can appear and a naive search can fail:
Alone: user#example.com
At the begin: user#example.com ...
At the end: ... user#example.com
In between: ... user#example.com ...
Now let’s analyze each variant:
To allow arbitrary input, you will need to escape the input properly. You can use the following method to do so:
RegExp.quote = function(str) {
return str.toString().replace(/(?=[.?*+^$[\]\\(){}-])/g, "\\");
};
To match all four cases, you can use the following pattern:
/(?:^|\ )user#example\.com(?![^\ ])/
Thus:
var inList = new RegExp("(?:^| )" + RegExp.quote(needle) + "(?![^ ])").test(haystack);
Using indexOf is a little more complex as you need to check the boundaries manually:
var pos = haystack.indexOf(needle);
if (pos != -1 && (pos != 0 && haystack.charAt(pos-1) !== " " || haystack.length < (pos+needle.length) && haystack.charAt(pos+needle.length) !== " ")) {
pos = -1;
}
var inList = pos != -1;
This one is rather quite simple:
var dict = {};
haystack.match(/[^\ ]+/g).map(function(match) { dict[match] = true; });
var inList = dict.hasOwnProperty(haystack);
Now to test what variant is the fastest, you can do that at jsPerf.

indexOf() is most probably the fastest just keep in mind you need to search for two possible cases:
var existingEmails = "email1, email2, ...";
var newEmail = "somethingHere#email.com";
var exists = (existingEmails.indexOf(newEmail + " ") >= 0) || (existingEmails.indexOf(" " + newEmail ) > 0);

You're asking a question with too many unstated variables for us to answer. For example, how many times do you expect to perform this search? only once? A hundred times? Is this a fixed list of emails, or does it change every time? Are you loading the emails with the page, or by AJAX?
IF you are performing more than one search, or the emails are loaded with the page, then you are probably best off creating a dictionary of the names, and using the Javascript in operator.
If you get the string from some off-page source, and you only search it once, then indexOf may well be better.
In all cases, if you really care about the speed, you're best off making a test.
But then I'd ask "Why do you care about the speed?" This is a web page, where loading the page happens at network speeds; the search happens at more or less local-processor speed. It's very unlikely that this one search will make a perceptible difference in the behavior of the page.

Here is a little explanation:
Performing a dictionary lookup is relatively complicated - very fast compared with (say) a linear lookup by key when there are lots of keys, but much more complicated than a straight array lookup. It has to calculate the hash of the key, then work out which bucket that should be in, possibly deal with duplicate hashes (or duplicate buckets) and then check for equality.
As always, choose the right data structure for the job - and if you really can get away with just indexing into an array (or List) then yes, that will be blindingly fast.
The above has been taken from one of the blog posts of #Jon Skeet.

I know this is an old question, but here goes an answer for those who might need in the future.
I made some tests and the indexOf() method is impossibly fast!
Tested the case on Opera 12.16 and it took 216µs to search and possibly find something.
Here is the code used:
console.time('a');
var a=((Math.random()*1e8)>>0).toString(16);
for(var i=0;i<1000;++i)a=a+' '+((Math.random()*1e8)>>0).toString(16)+((Math.random()*1e8)>>0).toString(16)+((Math.random()*1e8)>>0).toString(16)+((Math.random()*1e8)>>0).toString(16);
console.timeEnd('a');
console.time('b');
var b=(' '+a).indexOf(((Math.random()*1e8)>>0).toString(16));
console.timeEnd('b');
console.log([a,b]);
In the console you will see a huge output.
The timer 'a' counts the time taken to make the "garbage", and the timer 'b' is the time to search for the string.
Just adding 2 spaces, one before and one after, on the email list and adding 1 space before and after the email, you are set to go.
I use it to search for a class in an element without jQuery and it works pretty fast and fine.