We Keep Coding

How to avoid long for-loops for creating multiple arrays (javascript)

I´m stuck with a problem... given an input number I´m trying to output a string of length 4. The string has to be divided into 2 parameter sections "On"/"Off".
For example:
-If the input number is 16, then the string should get combined as follows:
"On" section = "On" * Math.floor(16/5) = 3 --> "On On On".
"Off" section should be: length-On-section = 4-3 = 1 --> "Off".
Hence the string should look like "On On On Off".
I´m currently trying to narrow my solution to a nicer approach than using a for loop. I have to repeat this process various times in my function to create strings following the same approach but in various lengths and "On"/"Off" section ratios. but I´m not sure how to set it up properly..
this is one example:
function hoursTop(hour) {
var lights = [], on = Math.floor(hour/5), off = 4 - topLightsOn;
for(var i=1; i<=on; i++){
lights.push('On');
}
for(var j=1; j<=Off; j++){
lights.push('Off');
}
return lights.join("");
}
This produces way too much code overall.. Thanks for helping me out!

You can use String#repeat to create the strings, then concat them, and trim the extra spaces:
function hoursTop(hour) {
var on = Math.floor(hour/5), off = 4 - on;
return 'on '.repeat(on) + 'off '.repeat(off).trim();
}
console.log(hoursTop(16));
Or you can use Array#fill to create the array, then concat them, and join the array to a string:
function hoursTop(hour) {
var on = Math.floor(hour/5), off = 4 - on;
return Array(on).fill('on').concat(Array(off).fill('off')).join(' ');
}
console.log(hoursTop(16));

Letters to predefined numbers conversion in one window

)
I have searched high and low, but i can´t find what i need. Or i´m to stupid to get it right ;-)
I need a page with several input boxes where i can type some text, and then an output area below each input, that shows the text converted to some predefined numbers.
example:
input: abcde fghi æøå (i need all kinds of characters like .,/: etc.)
output: 064 065 066 067 068 032
So it needs to convert like this:
"a"="064 "
"b"="065 "
"space"="032 "
(and yes, each number in output needs to be separated, or a space added after each number)
I have tried some different cipher guides in both php and javascript, but can´t get it to work. I did do an Excel document that could do some of it, but it had a limited amount of characters it could convert, then it started behaving weird. So i thought maybe PHP was the answer!
Any help is very appreciated
/Rasmus

In the spirit of elclanrs deleted answer, and for posterity:
<script>
// Using standard for loop
function stringToCharcodes(s) {
var result = [];
function pad(n){ return (n<10? '00' : n<100? '0' : 0) + n;}
for (var i=0, iLen=s.length; i<iLen; i++) {
result.push(pad(s.charCodeAt(i)));
}
return result.join(' ');
}
// Using ES5 forEach
function stringToCharcodes2(s) {
var result = [];
function pad(n){ return (n<10? '00' : n<100? '0' : 0) + n;}
s.split('').forEach(function(a){result.push(pad(a.charCodeAt(0)))});
return result.join(' ');
}
</script>
<input onkeyup="document.getElementById('s0').innerHTML = stringToCharcodes(this.value);"><br>
<span id="s0"></span>
Edit
If you want a custom mapping, use an object (I've only included 2 characters, you can add as many as you want):
var mapChars = (function() {
var mapping = {'198':'019', '230':'018'};
return function (s) {
var c, result = [];
for (var i=0, iLen=s.length; i<iLen; i++) {
c = s.charCodeAt(i);
result.push(c in mapping? mapping[c] : c);
}
return result.join(' ');
}
}());
alert(mapChars('Ææ')); //
Using the character code for mapping seems to be a reasonable solution, using the actual character may be subject to different page character encoding.

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.

Parse HTML source for dollar amounts then set highest amount as var

I need a JavaScript function that will parse the HTML source of the page from which it is called as an external script, retrieve any dollar amounts in the source, and set the highest dollar amount to a JavaScript variable.
So for instance, if the page contains the text, "Your product is $40.32 and tax is $4.50, your total is $44.82.", the JS should parse those values and set $44.82 to "var total" as the highest amount. Possible?

Thanks based on the tips I wrote this, which works. Hopefully yours or my solution will help others:
var dochtml = document.getElementsByTagName('body')[0].innerHTML;
dochtml = dochtml.replace(/(\r\n|\n|\r)/gm,"");
var price_array = new Array;
var pattmatch = /(\$(([0-9]{0,1})?.[0-9]{1,2}))|(\$([1-9]{1}[0-9]{0,2}([,][0-9]{3})*)(.[0-9]{1,2})?)/gi;
price_array = dochtml.match(pattmatch);
if (price_array) {
for (var i=0; itotal || !total) {
var total=price_array[i];
}
}
document.write(total);
}

You can grab the HTML of the current document from the Javascript by grabbing the document's innerHtml, something like:
document.getElementsByTagName('html')[0].innerHTML
Then you can pull out all the currency values with a regular expression, something like:
((\$(([0-9]{0,1})?\.[0-9]{1,2}))|(\$([1-9]{1}[0-9]{0,2}([,][0-9]{3})*)(\.[0-9]{1,2})?))
Just loop through all the matches and every time the current match is greater than the value in total, set total to the current match.
Disclaimer: That regex was pulled from the community on http://gskinner.com/RegExr/ and I can't promise you it's 100% fullproof.

Take a look at this question here, which demonstrates how to extract numbers from a String: Javascript extracting number from string
Try this:
// get all content from page
var content = document.body.innerHTML;
// create an array of all dollar amounts in the content
arrayNum = content.match(/\$[0-9]+\.[0-9]+/g);
// display array of numbers
console.info(arrayNum);
var high = 0;
for(var i = 0; i < arrayNum.length; i++) {
// remove the dollar sign and cast the string to a float
arrayNum[i] = parseFloat(arrayNum[i].substring(1));
// get the high value - O(n) operation
high = ( (arrayNum[i]) > high ) ? arrayNum[i] : high;
}
alert("High value = " high);

JavaScript filtering an array of <input> values by character count

This should be a quickie, but I'm scratching my head as to why this bit of JavaScript isn't working for me. The goal is to take the value of an input box (string of words separated by spaces), list these words as items in an array, and remove those which are fewer than 3 characters:
var typed = $('input').val();
var query = typed.split(" ");
var i=0;
for (i=0; i<query.length; i++) {
if (query[i].length < 3) {
query.splice(i,1);
}
}
Have this running onkeyup for the input box and it seems to work, but only about 50% of the time (strings of 1 and 2 characters somehow find their way into the array on occasion). Any suggestions would be hugely appreciated.

The problem is that you are iterating while removing the elements. Consider this array:
["he", "l", "lo world"]
Initially your loop starts at index 0 and removes "he" from the array. Now the new array is
["l", "lo world"]
In the next iteration i will be 1, and you will check "lo world"'s length, thus ignoring the "l" string altogether.
Use the filter method in Array to remove the unwanted elements.
var biggerWords = query.filter(function(word) {
return word.length >= 3;
});

Besides the iterating problem, you may also see unexpected entries if you type multiple spaces
try
var query = typed.split(/\s+/);
This way it will split on any number of spaces, instead of each individual one

The problem is that you're slicing the array while counting forward. Think about it...if you take an index point out of the array, thereby shortening it by one, incrementing i and moving on to the next one actually moves one further than you want, completely missing the next index. Increment i--, start at query.length-1, and make the condition that i>=0. For an example of this in action, check it out here:
http://jsfiddle.net/kcwjs/
CSS:
input {
width:300px;
}​
HTML:
<input id="textbox" type="text" />
<div id="message"></div>​
Javascript:
$(document).ready(function() {
$('#textbox').keyup(checkStrings);
});
function checkStrings(e) {
var typed = $('#textbox').val();
if (typed == "") return false;
var query = typed.split(" ");
var querylen = query.length;
var acceptedWords = '';
var badWords = '';
for (var i = querylen-1; i >= 0; i--) {
if (query[i].length < 3) {
badWords += query[i] + " ";
} else {
acceptedWords += query.splice(i,1) + " ";
}
}
$('#message').html("<div>Bad words are: " + badWords + "</div>" +
"<div>Good words are: " + acceptedWords + "</div>");
}

Try this code, it get's rid of any 3 character words, as well as making sure no empty array elements are created.
typed.replace(/(\b)\w{1,3}\b/g,"$1");
var query = typed.split(/\s+/);

hey i think you should use a new array for the result. since you are removing the element in array. the length is changed. here is my solution
var typed = "dacda cdac cd k foorar";
var query = typed.split(" ");
var i=0;
var result = [];
for (i=0; i<query.length; i++) {
if (query[i].length >= 3) {
result.push(query[i]);
}
}