Develop Reference

Perform a merge on two strings

I'm trying to build a collaborative doc editor and implement operational transformation. Imagine we have a string that is manipulated simultaneously by 2 users. They can only add characters, not remove them. We want to incorporate both of their changes.
The original string is: catspider
The first user does this: cat<span id>spider</span>
The second user does this: c<span id>atspi</span>der
I'm trying to write a function that will produce: c<span id>at<span id>spi</span>der</span>
The function I've written is close, but it produces c<span id>at<span i</span>d>spider</span> codepen here
String.prototype.splice = function(start, newSubStr) {
return this.slice(0, start) + newSubStr + this.slice(start);
};
function merge(saved, working, requested) {
if (!saved || !working || !requested) {
return false;
}
var diffSavedWorking = createDiff(working, saved);
var diffRequestedWorking = createDiff(working, requested);
var newStr = working;
for (var i = 0; i < Math.max(diffRequestedWorking.length, diffSavedWorking.length); i++) {
//splice does an insert `before` -- we will assume that the saved document characters
//should always appear before the requested document characters in this merger operation
//so we first insert requested and then saved, which means that the final string will have the
//original characters first.
if (diffRequestedWorking[i]) {
newStr = newStr.splice(i, diffRequestedWorking[i]);
//we need to update the merge arrays by the number of
//inserted characters.
var length = diffRequestedWorking[i].length;
insertNatX(diffSavedWorking, length, i + 1);
insertNatX(diffRequestedWorking, length, i + 1);
}
if (diffSavedWorking[i]) {
newStr = newStr.splice(i, diffSavedWorking[i]);
//we need to update the merge arrays by the number of
//inserted characters.
var length = diffSavedWorking[i].length;
insertNatX(diffSavedWorking, length, i + 1);
insertNatX(diffRequestedWorking, length, i + 1);
}
}
return newStr;
}
//arr1 should be the shorter array.
//returns inserted characters at their
//insertion index.
function createDiff(arr1, arr2) {
var diff = [];
var j = 0;
for (var i = 0; i < arr1.length; i++) {
diff[i] = "";
while (arr2[j] !== arr1[i]) {
diff[i] += arr2[j];
j++;
}
j++;
}
var remainder = arr2.substr(j);
if (remainder) diff[i] = remainder;
return diff;
}
function insertNatX(arr, length, pos) {
for (var j = 0; j < length; j++) {
arr.splice(pos, 0, "");
}
}
var saved = 'cat<span id>spider</span>';
var working = 'catspider';
var requested = 'c<span id>atspi</span>der';
console.log(merge(saved, working, requested));
Would appreciate any thoughts on a better / simpler way to achieve this.

Javascript: using a for statement as a variable

I'm fairly new to javascript and something I've been playing with lately is the 'for' statement. I'm questioning one thing, though. I've learned how to make a 'for' statement do things as if it was an output, like this:
for (i = 0; i < 3; i++) {
console.log(i);
}
But what if you want to set a variable for the whole output of the 'for' statement?
var destinationArray = ["town", "areas", "bosses"];
var destinationArraySet = 1;
var i;
for ( i = 0; i < destinationArraySet; i++) {
console.log(destinationArray[i]);
} /*the whole thing should be equal to var destination */
var userDestinationPrompt = ("Where would you like to go? Available places: " +
/* var destination */
+
".").toUpperCase();
To give some more context: I'm making a game that allows further destinations when the destination before is cleared. Once that's achieved, I set destinationArraySet to a higher value, which means that more places would be logged and put after 'Available places'.
Help would be very appreciated! If there's something not clear enough let me know.

The for statement is not an expression, so it doesn't have a return value. Use a variable to collect values in the loop:
var destination = '';
for (var i = 0; i < destinationArraySet; i++) {
destination += destinationArray[i] + ' ';
}
Of course, if you only want to concatenate the values in part of an array, you can use the slice method to get part of it, then the join method:
var destination = destinationArray.slice(0, destinationArraySet).join(' ');

var destination = '';
var destinationArray = ["town", "areas", "bosses"];
var destinationArraySet = 1;
for (var i = 0; i < destinationArraySet; i++) {
destination += destinationArray[i] + '\n';
}
console.log(destination);

Try this -
var destinationArray = ["town", "areas", "bosses"];
var destinationArraySet = 1;
var i;
var availablePlaces = '';
var separator = '';
for ( i = 0; i < destinationArraySet; i++) {
availablePlaces += separator + destinationArray[i];
separator = ', ';
}
var userDestinationPrompt = ("Where would you like to go? Available places: " +
availablePlaces + ".").toUpperCase();

The for statement doesn't have an "output", it's not a function. Thinking for as a function will give you troubles later on. for is simply a statement that continuously execute the block of code inside. It does not "output", or in other words, return any value.
Do this instead:
var destinationArray = ["town", "areas", "bosses"], destinationArraySet = 1;
var userDestinationPrompt = ("Where would you like to go? Available places: " +
destinationArray.slice(0, destinationArraySet).join("\n")
+ ".").toUpperCase();
prompt(userDestinationPrompt);
Demo: http://jsfiddle.net/7c2b9q7m/1/
destinationArray.slice(0, destinationArraySet): Cuts the array to the specified length.
.join("\n"): Join the newly created array by \ns (newline) to micic the default console.log behavior.

Each key value, join values inside loop

So i have a string, and I'm trying to join the content; if the val length is less than 10 chars, join it with the next value. But when i try this code, it joins with the same val instead of the next one.
//Set the regex.
myregex = /(<p>.*?<\/p>)/g;
//Variable string.
content = Example: <p>Hello</p><p>This is my test content</p><p>etc</p>
$(content.match(myregex)).each(function (key, val) {
var test = $(val).text();
if (test.length < 10) {
var n = val.concat(val);
$('#mydiv').append('<div>' + n + '</div>');
} else {
$('#mydiv').append('<div>' + val + '</div>');
}
})

This line here: val.concat(val), is indeed duplicating your content. What you need to do is grab the next value from the regex instead of the current one. Something like the following should work.
var matches = content.match(myregex),
myDiv = $('#mydiv');
for (var i = 0, len = matches.length; i < len; i++){
if (i + 1 < len && matches[i].length < 10){
myDiv.append('<div>' + matches[i].concat(matches[i+1]) + '</div>');
i += 1;
}
else myDiv.append('<div>' + matches[i] + '</div>');
}

val and val are the same thing, so of course val.concat(val) will duplicate it.
If you want to use $.each, I think it might be better to join with the previous value, because you don't know what the next one will be yet.
var previous = [];
$(content.match(myregex)).each(function (key, val) {
var test = $(val).text();
if (test.length < 10) {
previous = val;
} else {
if(previous.length) {
val = previous.concat(val);
}
$('#mydiv').append('<div>' + val + '</div>');
previous = [];
}
});

Need help w/ JavaScript and creating an html table from array

I've tried everything I can find via google and nothing has worked correctly. Output is just a single row with all the contents of the array listed. What I need is a way to write the contents of an array but after 3 cells, automatically start a new line. I'll post the code I've made below as well as the question. (yes this is from an assignment. :( )
//***(8) place the words in the string "tx_val" in a table with a one pixel border,
//*** with a gray backgound. Use only three cells per row. Empty cells should contain
//*** the word "null". Show the table in the span block with id="ans8"
var count = i % 3;
var nrow = "";
var out = "<table border='1' bgcolor='gray'><tr>"
for (var i=0; i<txArr.length; i++)
{
out += ("<td>" + txArr[i] + "</td>");
count++;
if (count % 3 == 0)
{
nrow += "</tr><tr>";
}
}
document.getElementById('ans8').innerHTML = out + nrow;

you need to print the tr's inside the table (annd add a </table>!):
var count = i % 3; // btw. what's this??
var nrow = "";
var out = "<table border='1' bgcolor='gray'><tr>"
for (var i=0; i<txArr.length; i++)
{
out += "<td>" + txArr[i] + "</td>";
count++;
if (count % 3 == 0)
out += "</tr><tr>";
}
out += "</table>";
document.getElementById('ans8').innerHTML = out;

Rather than try to write out the html, try manipulating the dom. It seems much more straightforward to me. Take a look at the following:
var row = table.insertRow();
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var cell = row.insertCell();
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var cellContent = document.createTextNode(txArr[i]);
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cell.appendChild(cellContent);
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For deciding when to start a new row, just use the modulus operator (%
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) against i:
if (i % 3 == 0)
{
row = table.insertRow()
}
You'd end up with something like this:
var container = document.getElementById("ans8");
var t = container.appendChild(document.createElement("table"));
var row;
txArr.forEach(function (item, i)
{
if (i % 3 == 0)
{
row = t.insertRow()
}
row.insertCell().appendChild(document.createTextNode(item));
});
I'll leave a little for you to figure out - border, background color, getting the word "null" in there. It is your homework after all. :-)
Also, for older browsers you'll need to add Array.forEach in yourself.

I prefer using an array over concatination
var html = [];
html.push("<table><tr>");
var i = 0;
for (var k in txArr)
{
if(i>=3){
i=0;
html.push("</tr><tr>");
}
html.push("<td>" + txArr[k] + "</td>");
i++;
}
html.push("</tr></table>");
document.getElementById('ans8').innerHTML = html.join('');
// wrapped in function
function arrayToTable(a,cols){
var html = [];
html.push("<table><tr>");
var i = 0;
for (var k in a)
{
if(i>=cols){
i=0;
html.push("</tr><tr>");
}
html.push("<td>" + a[k] + "</td>");
i++;
}
html.push("</tr></table>");
return html.join('')
}
document.getElementById('ans8').innerHTML = arrayToTable(txArr, 3);

It might be a tad easier to accomplish with something like
buffer = "<table>";
for(var r = 0; r < 10; r++){
buffer += "<tr>";
for(var c = 0; c < 3 ; c++){
buffer += "<td>Cell: " + r + ":" + c + "</td>";
}
buffer += "</tr>";
}
buffer += "</table>";
document.getElementById("ans8").innerHTML = buffer;
That would create a table 30 rows long by 3 columns for each row.

you might be assigning values to "count" too early as you don't know what i is yet. and you are not spitting out the value of nrow anywhere... change it to out.
var count;
var nrow = "";
var out = "<table border='1' bgcolor='gray'><tr>"
for (var i=0; i<txArr.length; i++)
{
out += ("<td>" + txArr[i] + "</td>");
count++;
if (count % 3 == 0)
{
out += "</tr><tr>";
}
}
document.getElementById('ans8').innerHTML = out + nrow;

Basically I would split it up into 3 functions, for readability and maintenance. These functions would consist of creating a cell, a row, and a table. This definitely simplifies reading the code. As I have not tested it, below is an example of what I would do.
function createTableCell(value) {
return value == null? "<td>NULL</td>":"<td>" + value + "</td>";
}
function createTableRow(array) {
var returnValue = "";
for (var i = 0; i < array.length; i++) {
returnValue = returnValue + createTableCell(array[i]);
}
return "<tr>" + returnValue + "</tr>";
}
function arrayToTable(array, newRowAfterNArrayElements) {
var returnValue = "<table>";
for (var i = 0; i < array.length; i = i + newRowAfterNArrayElements) {
returnValue = returnValue + createTableRow(array.split(i, (i + newRowAfterNArrayElements) - 1));
}
return returnValue + "</table>";
}
document.getElementById("ans8").innerHTML = arrayToTable(txArr, 3);
In addition this makes your code much more dynamic and reusable. Suppose you have an array you want to split at every 4 element. Instead of hardcoding that you can simply pass a different argument.

Here's a live example of doing this with DOMBuilder, and of using the same code to generate DOM Elements and an HTML String.
http://jsfiddle.net/insin/hntxW/
Code:
var dom = DOMBuilder.elementFunctions;
function arrayToTable(a, cols) {
var rows = [];
for (var i = 0, l = a.length; i < l; i += cols) {
rows.push(a.slice(i, i + cols));
}
return dom.TABLE({border: 1, bgcolor: 'gray'},
dom.TBODY(
dom.TR.map(rows, function(cells) {
return dom.TD.map(cells);
})
)
);
}
var data = [1, 2, null, 3, null, 4, null, 5, 6];
document.body.appendChild(arrayToTable(data, 3));
document.body.appendChild(
dom.TEXTAREA({cols: 60, rows: 6},
DOMBuilder.withMode("HTML", function() {
return ""+arrayToTable(data, 3);
})
)
);

Yes, you can build from scratch...but there's a faster way. Throw a grid at it. The grid will take data in a string, array, json output, etc and turn it into a proper HTML outputted table and will allow you to extend it with sorting, paging, filtering, etc.
My personal favorite is DataTables, but there are numerous others out there.
Once you get proficient, setting one of these up literally takes 5 minutes. Save your brain power to cure world hunger, code the next facebook, etc....

Search Array in JavaScript

I need to sort through a data set which as you can see I've assigned to the records variable. From that data I need to see if the zip code exists. If the zip code does not exist then I need to move it into the array (There of course will be duplicates) and continue checking the rest of the records, if it does exist I need to do nothing.
// Declare Array
var numbersArray = [];
// Variables
var records;
var zipCode;
var numbers;
var index;
var output;
var outputMessageOne;
var outputMessageTwo;
var count = 0;
output = document.getElementById('outputDiv');
records = openZipCodeStudyRecordSet();
output.innerHTML = "The unique zip codes are: ";
while (records.readNextRecord()) {
zipCode = records.getSampleZipCode();
for (index = 0; index < numbersArray.length; index++) {
if (zipCode === numbersArray[index]) {
var uniqueZip = false;
break;
records++;
}
if (zipCode !== numbersArray[index]) {
numbersArray.push(zipCode);
}
}
output.innerHTML += numbersArray;
}
}

You can simplify your for loop like so:
matchedZip = false;
for(i in numbersArray) {
if (numbersArray[i] === zipCode) {
matchedZip = true;
}
}
if ( ! matchedZip) {
numbersArray.push(zipCode);
}
Try plugging that into your while loop. If you have the array push inside of the for loop you're going to end up pushing each zip code in every time there is not a match.

Well, you didn't exactly ask a question, but I'll answer anyway :) The answer is that you should not use a normal array for this, but rather a map or associative array. Fortunately a plain Javascript object can be used for this:
var numbers = {};
// Variables
var records;
var numbers;
var index;
var output;
var outputMessageOne;
var outputMessageTwo;
var count = 0;
output = document.getElementById('outputDiv');
records = openZipCodeStudyRecordSet();
output.innerHTML = "The unique zip codes are: ";
while (records.readNextRecord()) {
var zipCode = records.getSampleZipCode();
numbers[zipCode] = 1; // just picking an arbitrary value
}
for (var zipCode: numbers) {
output.innerHTML += zip + " ";
}
The reason is that this way you don't need to loop through the existing data for each new input.