Develop Reference

Replace string in JS array without using native replace() method

I am stuck a bit with replacing string in js array. I am trying to log the arguments to see what is going on but am missing a piece of the puzzle.
fiddle
// - trying to look for substring in array
// - if match is found
// - replace substring without using the native method replace();
var div = $('.insert');
data = ["erf,", "erfeer,rf", "erfer"];
data = data.map(function (x) {
return /""/g.test(x) ? x.replace(/""/g, "") : x
});
function fakeReplace(data, substr, newstr) {
//should show ["erf,", "erfeer,rf", "erfer"];
div.append("data before match replace = " + data);
div.append("\<br>");
div.append("substr = " + substr);
div.append("\<br>");
div.append("newstr = " + newstr);
div.append("\<br>");
return data.split(substr).join(newstr);
}
fakeReplace(data, "erf", "blue");
//should show ["blue,", "blueeer,rf", "blueer"];
div.append("data after fakeReplace is executed = " + data);

You are treating data like a string in your function. You can use map() to return a new array with each element replaced.
function fakeReplace(data, substr, newstr) {
return data.map(function(s) {
return s.split(substr).join(newstr);
})
}

let myString = "Victor";
let splitted = myString.split('');
function replaceManual(a,b){
for(let i = 0; i<= splitted.length-1; i++)
{
for(let j=i; j <=i;j++)
{
if(splitted[j]===a)
{
splitted[j]=b;
return splitted;
}
else
{
break;
}
}
}
}
replaceManual('V','T');
console.log(splitted.toString().replace(/[^\w\s]/gi, ''));

How can I group data returned in JSON format and return it?

I have a JSON string of the form:
[
{"ID":153,"CircuitID":53,"StartTime":"2014-11-12 12:45:00","EventFormatID":224,"TotalPlaces":8,"BookedPlaces":0,"ProvisionalPlaces":0},
{"ID":161,"CircuitID":53,"StartTime":"2014-11-12 17:15:00","EventFormatID":224,"TotalPlaces":0,"BookedPlaces":0,"ProvisionalPlaces":0},
{"ID":734,"CircuitID":53,"StartTime":"2014-11-12 18:30:00","EventFormatID":231,"TotalPlaces":14,"BookedPlaces":0,"ProvisionalPlaces":0}
]
In place of Event Format ID and Circuit ID I will be returning the names
What I need to do is group the results by Event Format ID and return the results in the following format:
Event 224 : 12:45 (8 places available), 17:15 (0 places available)
Event 231 : 18:30 (14 places available)
I can't seem to figure out how to loop through the data, group it by Event Format ID to present it in the required format!
Thanks

Can you use any additional libraries? I'd use lo-dash which would make this relatively simple:
var grouped = _.groupBy(data, "EventFormatID");
_(grouped).forEach(function (group, key) {
console.log("Event:" + key);
_(group).forEach(function (course) {
console.log(course.StartTime + " (" + course.TotalPlaces + " places available)");
});
});
Obviously the example above logs to the console but it'd be fairly simple to change to build up whatever string or object you need.

This is easier with lodash/underscore, or even with ES5 array and object methods, but since you asked about pure JS:
var data = {}, results = [], i, j, id, time, obj, evts; // obj is your object above
for (i=0; i<obj.length; i++) {
id = obj[i].EventFormatID;
time = obj[i].StartTime; // you can simplify to get just the time, not the datetime, if you prefer
data[id] = data[id] || [];
data[id].push({"time":time,"places":obj[i].TotalPlaces});
}
// now you have a proper data structure, just print it out
for (i in data) {
if (data.hasOwnProperty(i)) {
// just show the output properly formatted
evts = [];
for (j=0;i<data[i].length;j++) {
evts.push(data[i][j].time+" ("+data[i][j].places+" places available)");
}
results.push("Event "+i+" : "+evts.join(","));
}
}
ES5 makes this so much easier
var data = {}, results = [], obj; // obj is your object above
obj.forEach(function(val,i) {
data[val.EventFormatID] = data[val.EventFormatID] || [];
data[val.EventFormatID].push({"time":val.StartTime,"places":val.TotalPlaces});
});
// now you have a proper data structure, just print it out
Object.keys(data).forEach(function(key) {
var value = data[key], evts = [];
value.forEach(function(elm) {
evts.push(elm.time+" ("+elm.places+" places available)");
});
results.push("Event "+key+" : "+evts.join(","));
});
And lodash is even easier.

Please take a look that:
http://jsfiddle.net/m260n5ud/
html
<div id="contentDiv"></div>
js
function tidyUp(jsonArray) {
var myObject = {};
for (i = 0; i < jsonArray.length; i++) {
var key = jsonArray[i]['EventFormatID'];
var time = jsonArray[i]['StartTime'].replace(' ', ':').split(/[- :]/);
time = time[3] + ":" + time[4];
var totalPlace = jsonArray[i]['TotalPlaces'];
if (myObject[key] == null) {
myObject[key] = "Event : " + key + " : " + time + " ( " + totalPlace + " places available)";
} else {
myObject[key] += ", " + time + " ( " + totalPlace + " places available)";
}
}
console.log(myObject);
for (var k in myObject) {
document.getElementById('contentDiv').innerHTML += myObject[k] + "<br/>";
}
}

Javascript: randomly pair items from array without repeats

I am trying to make a very basic "secret santa" generator as one of my first Javascript projects. I have searched for hours for a solution to this problem but so far nothing has worked that I have found.
I have an array of names which need paired to each other. I successfully have them pairing to each other, but right now someone can be drawn twice. I am pushing the randomly chosen names to another array but I can't find a way to check the randomly chosen names against the ones already chosen.
var names = ["Sean","Kyle","Emily","Nick","Cotter","Brian","Jeremy","Kimmy","Pat","Johnny"];
var used = [];
var picks = [];
if (names.length % 2 != 0) {
alert("You must have an even number of names. You currently have " + names.length + " names.");
}
for( var i = 0; i < names.length; i++){
var random = Math.floor(Math.random()*names.length)
if(names[random] == names[i]) {
names[random] = names[random++];
picks.push(names[i] + " gets " + names[random]);
used.push(names[random]);
} else {
picks.push(names[i] + " gets " + names[random]);
used.push(names[random]);
}
}
console.log("picked array: ")
for(var k=0; k<picks.length; k++) {
console.log(picks[k]);
}
console.log("used array: " + used);
Thank you in advance for any help.

Create two arrays with the names, shuffle them, and make sure you don't pick the same name from both arrays :
var names = ["Sean","Kyle","Emily","Nick","Cotter","Brian","Jeremy","Kimmy","Pat","Johnny"];
if (names.length % 2 != 0) {
alert("You must have an even number of names. You currently have " + names.length + " names.");
} else {
var arr1 = names.slice(), // copy array
arr2 = names.slice(); // copy array again
arr1.sort(function() { return 0.5 - Math.random();}); // shuffle arrays
arr2.sort(function() { return 0.5 - Math.random();});
while (arr1.length) {
var name1 = arr1.pop(), // get the last value of arr1
name2 = arr2[0] == name1 ? arr2.pop() : arr2.shift();
// ^^ if the first value is the same as name1,
// get the last value, otherwise get the first
console.log(name1 + ' gets ' + name2);
}
}
FIDDLE

I would suggest a different approach. Shuffle, split, and zip, no mutation:
var splitAt = function(i, xs) {
var a = xs.slice(0, i);
var b = xs.slice(i, xs.length);
return [a, b];
};
var shuffle = function(xs) {
return xs.slice(0).sort(function() {
return .5 - Math.random();
});
};
var zip = function(xs) {
return xs[0].map(function(_,i) {
return xs.map(function(x) {
return x[i];
});
});
}
// Obviously assumes even array
var result = zip(splitAt(names.length/2, shuffle(names)));
//^
// [
// [ 'Nick', 'Kimmy' ],
// [ 'Sean', 'Johnny' ],
// [ 'Kyle', 'Brian' ],
// [ 'Cotter', 'Pat' ],
// [ 'Emily', 'Jeremy' ]
// ]

There is a multitude of ways you can achieve this.
The fastest to code, but not necessarily the randomest is:
var names = ["Sean","Kyle","Emily","Nick","Cotter","Brian","Jeremy","Kimmy","Pat","Johnny"];
function getPicks(names) {
return names.slice(0).sort(function(){ return Math.random()-0.5 }).map(function(name, index, arr){
return name + " gets " + arr[(index+1)%arr.length];
});
}
getPicks(names);
This is not very random because the shuffling isn't very good and also because you get a single cycle each time. There can be no two cycles A->B->C->A D->E->D.
If you want it to have a random number of cycles of variable length, you can split the names array in several arrays and do the above for each of them, then concatenate the results (see elclanrs).
Finally, the last solution is for each person to pick a person at random and if it's the same one, simply pick again. If the last name remaining in both arrays is the same, simply swap it with another pair.
var names = ["Sean","Kyle","Emily","Nick","Cotter","Brian","Jeremy","Kimmy","Pat","Johnny"];
var a = names.slice(0);
var b = names.slice(0);
var result = [];
while (a.length > 1) {
var i = extractRandomElement(a);
var j = extractRandomElement(b);
while (i===j) {
b.push(j);
j = extractRandomElement(b);
}
result.push({ a:i, b:j });
}
if (a[0] === b[0]) {
result.push({ a:a[0], b:result[0].b });
result[0].b = a[0];
} else {
result.push({ a:a[0], b:b[0] });
}
var pairs = result.map(function(item){ return item.a + ' gets ' + item.b});
function extractRandomElement(array) {
return array.splice(Math.floor(Math.random()*array.length),1)[0];
}

I'm a tad late, but thought I'd throw my answer in here. It essentially does the same thing #adeneo's does, but it uses the same basic code as OP:
var names = ["Sean","Kyle","Emily","Nick","Cotter","Brian","Jeremy","Kimmy","Pat","Johnny"];
pickpool = names.slice(0); // Slice the array at the first element to copy it by value
var used = [];
var picks = [];
if (names.length % 2 != 0) {
alert("You must have an even number of names. You currently have " + names.length + " names.");
}
for( var i = 0; i < names.length; i++){
var random = Math.floor(Math.random()*pickpool.length)
if(names[random] == names[i]) {
// names[random] = names[random++];
picks.push(names[i] + " gets " + pickpool[random++]);
pickpool.splice(random++,1);
} else {
picks.push(names[i] + " gets " + pickpool[random]);
pickpool.splice(random,1);
}
}
console.log("picked array: ");
for(var k=0; k<picks.length; k++) {
console.log(picks[k]);
}
http://jsfiddle.net/SNJpC/

If you don't need to keep the original array you can remove the names as they get selected and each time you pick a name check that it isn't an empty string before pushing it to the next array.

Another consideration...
If you are trying to make a 'Secret Santa' generator, by using random method you can get the same pair next year, and next...
This is another solution where you get all the possible pairs (without repeating a name itself or a pair) for multiple years.
var names = ["Sean", "Kyle", "Emily", "Nick", "Cotter", "Brian", "Jeremy", "Kimmy", "Pat", "Johnny"];
if (names.length % 2 != 0) {
alert("You must have an even number of names. You currently have " + names.length + " names.");
} else {
const arr1 = names.slice()
let arr2 = names.slice();
let countDown = number => {
if (number === 1) {
return;
}
const last = arr2.pop([number - 1]);
arr2.unshift(last);
let pairs = [];
arr1.map(item => {
const index = arr1.indexOf(item);
pairs.push(`${arr1[index]} gets ${arr2[index]}`)
})
console.log(pairs)
return countDown(number - 1);
}
countDown(names.length)
}

Get textual (string) version of an object - displaying in the browser for debugging purposes [duplicate]

I'm trying to find a way to "pretty print" a JavaScript data structure in a human-readable form for debugging.
I have a rather big and complicated data structure being stored in JS and I need to write some code to manipulate it. In order to work out what I'm doing and where I'm going wrong, what I really need is to be able to see the data structure in its entirety, and update it whenever I make changes through the UI.
All of this stuff I can handle myself, apart from finding a nice way to dump a JavaScript data structure to a human-readable string. JSON would do, but it really needs to be nicely formatted and indented. I'd usually use Firebug's excellent DOM dumping stuff for this, but I really need to be able to see the entire structure at once, which doesn't seem to be possible in Firebug.

Use Crockford's JSON.stringify like this:
var myArray = ['e', {pluribus: 'unum'}];
var text = JSON.stringify(myArray, null, '\t'); //you can specify a number instead of '\t' and that many spaces will be used for indentation...
Variable text would look like this:
[
"e",
{
"pluribus": "unum"
}
]
By the way, this requires nothing more than that JS file - it will work with any library, etc.

I wrote a function to dump a JS object in a readable form, although the output isn't indented, but it shouldn't be too hard to add that: I made this function from one I made for Lua (which is much more complex) which handled this indentation issue.
Here is the "simple" version:
function DumpObject(obj)
{
var od = new Object;
var result = "";
var len = 0;
for (var property in obj)
{
var value = obj[property];
if (typeof value == 'string')
value = "'" + value + "'";
else if (typeof value == 'object')
{
if (value instanceof Array)
{
value = "[ " + value + " ]";
}
else
{
var ood = DumpObject(value);
value = "{ " + ood.dump + " }";
}
}
result += "'" + property + "' : " + value + ", ";
len++;
}
od.dump = result.replace(/, $/, "");
od.len = len;
return od;
}
I will look at improving it a bit.
Note 1: To use it, do od = DumpObject(something) and use od.dump. Convoluted because I wanted the len value too (number of items) for another purpose. It is trivial to make the function return only the string.
Note 2: it doesn't handle loops in references.
EDIT
I made the indented version.
function DumpObjectIndented(obj, indent)
{
var result = "";
if (indent == null) indent = "";
for (var property in obj)
{
var value = obj[property];
if (typeof value == 'string')
value = "'" + value + "'";
else if (typeof value == 'object')
{
if (value instanceof Array)
{
// Just let JS convert the Array to a string!
value = "[ " + value + " ]";
}
else
{
// Recursive dump
// (replace " " by "\t" or something else if you prefer)
var od = DumpObjectIndented(value, indent + " ");
// If you like { on the same line as the key
//value = "{\n" + od + "\n" + indent + "}";
// If you prefer { and } to be aligned
value = "\n" + indent + "{\n" + od + "\n" + indent + "}";
}
}
result += indent + "'" + property + "' : " + value + ",\n";
}
return result.replace(/,\n$/, "");
}
Choose your indentation on the line with the recursive call, and you brace style by switching the commented line after this one.
... I see you whipped up your own version, which is good. Visitors will have a choice.

You can use the following
<pre id="dump"></pre>
<script>
var dump = JSON.stringify(sampleJsonObject, null, 4);
$('#dump').html(dump)
</script>

In Firebug, if you just console.debug ("%o", my_object) you can click on it in the console and enter an interactive object explorer. It shows the entire object, and lets you expand nested objects.

For Node.js, use:
util.inspect(object, [options]);
API Documentation

For those looking for an awesome way to see your object, check prettyPrint.js
Creates a table with configurable view options to be printed somewhere on your doc. Better to look than in the console.
var tbl = prettyPrint( myObject, { /* options such as maxDepth, etc. */ });
document.body.appendChild(tbl);

I'm programming in Rhino and I wasn't satisfied with any of the answers that were posted here. So I've written my own pretty printer:
function pp(object, depth, embedded) {
typeof(depth) == "number" || (depth = 0)
typeof(embedded) == "boolean" || (embedded = false)
var newline = false
var spacer = function(depth) { var spaces = ""; for (var i=0;i<depth;i++) { spaces += " "}; return spaces }
var pretty = ""
if ( typeof(object) == "undefined" ) { pretty += "undefined" }
else if ( typeof(object) == "boolean" ||
typeof(object) == "number" ) { pretty += object.toString() }
else if ( typeof(object) == "string" ) { pretty += "\"" + object + "\"" }
else if ( object == null) { pretty += "null" }
else if ( object instanceof(Array) ) {
if ( object.length > 0 ) {
if (embedded) { newline = true }
var content = ""
for each (var item in object) { content += pp(item, depth+1) + ",\n" + spacer(depth+1) }
content = content.replace(/,\n\s*$/, "").replace(/^\s*/,"")
pretty += "[ " + content + "\n" + spacer(depth) + "]"
} else { pretty += "[]" }
}
else if (typeof(object) == "object") {
if ( Object.keys(object).length > 0 ){
if (embedded) { newline = true }
var content = ""
for (var key in object) {
content += spacer(depth + 1) + key.toString() + ": " + pp(object[key], depth+2, true) + ",\n"
}
content = content.replace(/,\n\s*$/, "").replace(/^\s*/,"")
pretty += "{ " + content + "\n" + spacer(depth) + "}"
} else { pretty += "{}"}
}
else { pretty += object.toString() }
return ((newline ? "\n" + spacer(depth) : "") + pretty)
}
The output looks like this:
js> pp({foo:"bar", baz: 1})
{ foo: "bar",
baz: 1
}
js> var taco
js> pp({foo:"bar", baz: [1,"taco",{"blarg": "moo", "mine": "craft"}, null, taco, {}], bleep: {a:null, b:taco, c: []}})
{ foo: "bar",
baz:
[ 1,
"taco",
{ blarg: "moo",
mine: "craft"
},
null,
undefined,
{}
],
bleep:
{ a: null,
b: undefined,
c: []
}
}
I've also posted it as a Gist here for whatever future changes may be required.

jsDump
jsDump.parse([
window,
document,
{ a : 5, '1' : 'foo' },
/^[ab]+$/g,
new RegExp('x(.*?)z','ig'),
alert,
function fn( x, y, z ){
return x + y;
},
true,
undefined,
null,
new Date(),
document.body,
document.getElementById('links')
])
becomes
[
[Window],
[Document],
{
"1": "foo",
"a": 5
},
/^[ab]+$/g,
/x(.*?)z/gi,
function alert( a ){
[code]
},
function fn( a, b, c ){
[code]
},
true,
undefined,
null,
"Fri Feb 19 2010 00:49:45 GMT+0300 (MSK)",
<body id="body" class="node"></body>,
<div id="links">
]
QUnit (Unit-testing framework used by jQuery) using slightly patched version of jsDump.
JSON.stringify() is not best choice on some cases.
JSON.stringify({f:function(){}}) // "{}"
JSON.stringify(document.body) // TypeError: Converting circular structure to JSON

Taking PhiLho's lead (thanks very much :)), I ended up writing my own as I couldn't quite get his to do what I wanted. It's pretty rough and ready, but it does the job I need. Thank you all for the excellent suggestions.
It's not brilliant code, I know, but for what it's worth, here it is. Someone might find it useful:
// Usage: dump(object)
function dump(object, pad){
var indent = '\t'
if (!pad) pad = ''
var out = ''
if (object.constructor == Array){
out += '[\n'
for (var i=0; i<object.length; i++){
out += pad + indent + dump(object[i], pad + indent) + '\n'
}
out += pad + ']'
}else if (object.constructor == Object){
out += '{\n'
for (var i in object){
out += pad + indent + i + ': ' + dump(object[i], pad + indent) + '\n'
}
out += pad + '}'
}else{
out += object
}
return out
}

For anyone checking this question out in 2021 or post-2021
Check out this Other StackOverflow Answer by hassan
TLDR:
JSON.stringify(data,null,2)
here the third parameter is the tab/spaces

This is really just a comment on Jason Bunting's "Use Crockford's JSON.stringify", but I wasn't able to add a comment to that answer.
As noted in the comments, JSON.stringify doesn't play well with the Prototype (www.prototypejs.org) library. However, it is fairly easy to make them play well together by temporarily removing the Array.prototype.toJSON method that prototype adds, run Crockford's stringify(), then put it back like this:
var temp = Array.prototype.toJSON;
delete Array.prototype.toJSON;
$('result').value += JSON.stringify(profile_base, null, 2);
Array.prototype.toJSON = temp;

I thought J. Buntings response on using JSON.stringify was good as well. A an aside, you can use JSON.stringify via YUIs JSON object if you happen to be using YUI. In my case I needed to dump to HTML so it was easier to just tweak/cut/paste PhiLho response.
function dumpObject(obj, indent)
{
var CR = "<br />", SPC = " ", result = "";
if (indent == null) indent = "";
for (var property in obj)
{
var value = obj[property];
if (typeof value == 'string')
{
value = "'" + value + "'";
}
else if (typeof value == 'object')
{
if (value instanceof Array)
{
// Just let JS convert the Array to a string!
value = "[ " + value + " ]";
}
else
{
var od = dumpObject(value, indent + SPC);
value = CR + indent + "{" + CR + od + CR + indent + "}";
}
}
result += indent + "'" + property + "' : " + value + "," + CR;
}
return result;
}

Lots of people writing code in this thread, with many comments about various gotchas. I liked this solution because it seemed complete and was a single file with no dependencies.
browser
nodejs
It worked "out of the box" and has both node and browser versions (presumably just different wrappers but I didn't dig to confirm).
The library also supports pretty printing XML, SQL and CSS, but I haven't tried those features.

A simple one for printing the elements as strings:
var s = "";
var len = array.length;
var lenMinus1 = len - 1
for (var i = 0; i < len; i++) {
s += array[i];
if(i < lenMinus1) {
s += ", ";
}
}
alert(s);

My NeatJSON library has both Ruby and JavaScript versions. It is freely available under a (permissive) MIT License. You can view an online demo/converter at:
http://phrogz.net/JS/neatjson/neatjson.html
Some features (all optional):
Wrap to a specific width; if an object or array can fit on the line, it is kept on one line.
Align the colons for all keys in an object.
Sort the keys to an object alphabetically.
Format floating point numbers to a specific number of decimals.
When wrapping, use a 'short' version that puts the open/close brackets for arrays and objects on the same line as the first/last value.
Control the whitespace for arrays and objects in a granular manner (inside brackets, before/after colons and commas).
Works in the web browser and as a Node.js module.

flexjson includes a prettyPrint() function that might give you what you want.

What's the best way to count keywords in JavaScript?

What's the best and most efficient way to count keywords in JavaScript? Basically, I'd like to take a string and get the top N words or phrases that occur in the string, mainly for the use of suggesting tags. I'm looking more for conceptual hints or links to real-life examples than actual code, but I certainly wouldn't mind if you'd like to share code as well. If there are particular functions that would help, I'd also appreciate that.
Right now I think I'm at using the split() function to separate the string by spaces and then cleaning punctuation out with a regular expression. I'd also want it to be case-insensitive.

Cut, paste + execute demo:
var text = "Text to be examined to determine which n words are used the most";
// Find 'em!
var wordRegExp = /\w+(?:'\w{1,2})?/g;
var words = {};
var matches;
while ((matches = wordRegExp.exec(text)) != null)
{
var word = matches[0].toLowerCase();
if (typeof words[word] == "undefined")
{
words[word] = 1;
}
else
{
words[word]++;
}
}
// Sort 'em!
var wordList = [];
for (var word in words)
{
if (words.hasOwnProperty(word))
{
wordList.push([word, words[word]]);
}
}
wordList.sort(function(a, b) { return b[1] - a[1]; });
// Come back any time, straaanger!
var n = 10;
var message = ["The top " + n + " words are:"];
for (var i = 0; i < n; i++)
{
message.push(wordList[i][0] + " - " + wordList[i][1] + " occurance" +
(wordList[i][1] == 1 ? "" : "s"));
}
alert(message.join("\n"));
Reusable function:
function getTopNWords(text, n)
{
var wordRegExp = /\w+(?:'\w{1,2})?/g;
var words = {};
var matches;
while ((matches = wordRegExp.exec(text)) != null)
{
var word = matches[0].toLowerCase();
if (typeof words[word] == "undefined")
{
words[word] = 1;
}
else
{
words[word]++;
}
}
var wordList = [];
for (var word in words)
{
if (words.hasOwnProperty(word))
{
wordList.push([word, words[word]]);
}
}
wordList.sort(function(a, b) { return b[1] - a[1]; });
var topWords = [];
for (var i = 0; i < n; i++)
{
topWords.push(wordList[i][0]);
}
return topWords;
}

Once you have that array of words cleaned up, and let's say you call it wordArray:
var keywordRegistry = {};
for(var i = 0; i < wordArray.length; i++) {
if(keywordRegistry.hasOwnProperty(wordArray[i]) == false) {
keywordRegistry[wordArray[i]] = 0;
}
keywordRegistry[wordArray[i]] = keywordRegistry[wordArray[i]] + 1;
}
// now keywordRegistry will have, as properties, all of the
// words in your word array with their respective counts
// this will alert (choose something better than alert) all words and their counts
for(var keyword in keywordRegistry) {
alert("The keyword '" + keyword + "' occurred " + keywordRegistry[keyword] + " times");
}
That should give you the basics of doing this part of the work.

Try to split you string on words and count the resulting words, then sort on the counts.

This builds upon a previous answer by insin by only having one loop:
function top_words(text, n) {
// Split text on non word characters
var words = text.toLowerCase().split(/\W+/)
var positions = new Array()
var word_counts = new Array()
for (var i=0; i<words.length; i++) {
var word = words[i]
if (!word) {
continue
}
if (typeof positions[word] == 'undefined') {
positions[word] = word_counts.length
word_counts.push([word, 1])
} else {
word_counts[positions[word]][1]++
}
}
// Put most frequent words at the beginning.
word_counts.sort(function (a, b) {return b[1] - a[1]})
// Return the first n items
return word_counts.slice(0, n)
}
// Let's see if it works.
var text = "Words in here are repeated. Are repeated, repeated!"
alert(top_words(text, 3))
The result of the example is: [['repeated',3], ['are',2], ['words', 1]]

I would do exactly what you have mentioned above to isolate each word. I would then probably add each word as the index of an array with the number of occurrences as the value.
For example:
var a = new Array;
a[word] = a[word]?a[word]+1:1;
Now you know how many unique words there are (a.length) and how many occurrences of each word existed (a[word]).