Develop Reference

How should I properly assign a key and value pair?

JavaScript newbie. My code is working BUT I'm still getting this alert:
should_properly_assign_key_and_value_pair, Expected 'string' to be
'object'.
Not sure how update current code to address this issue. Any advice? Thank you!
function transformFirstAndLast(array) {
var result = '';
for (var i = 0; i < array.length; i++) {
result = (array[0] + ": " + array[array.length-1]);
return result;
}
}
console.log(transformFirstAndLast(['Kevin','Bacon','Spacey']));//Kevin : 'Spacey'

Since it is expecting a key/value pair. Create a new object and set the data.
Change
result = (array[0] + ": " + array[array.length-1]);
to
var result = {};
result[array[0]] = array[array.length-1];
return result;

It's hard to understand what your code wants to do? The current code will always return the first element and the last element in the array with a ':' in middle, regardless how many other elements in the array. Is that your intention? If yes, I think you don't need to the loop, right? just return array[0] + ':' + array[arraly.length - 1] does the job for you..
If your intention is to concatenate the elements in the array, your code need to be revised.

Populate a prompt with elements of an array and number them off

(Stack Overflow doesn't have a tag for 'prompt' so I have used alert as I am guessing it is similar enough to attract the right answerers.)
Hello,
I am currently making a JavaScript-based game for an assignment at university. I am usually pretty good with problem solving but have been stumped by this issue.
To explain, I have an array which names the possible armour slots the player can pick. In any order these can be picked, and each time the choice gets pushed to a second array which handles what has already been picked (and in what order) and that item gets spliced from the original array. There is a while loop which runs through until all 3 have been picked.
var armourSlotToPick = ["Head", "Chest", "Legs"],
armourSlotPicked = [],
armourLoop = 1,
indexArmour = 0;
function numInArray() {
indexArmour++;
return (indexArmour + ". " + armourSlotToPick[indexArmour - 1] + "\n");
}
function armour() {
while (armourLoop < 4) {
var armourPick = prompt("Pick an armour slot to generate an item for:\n" + armourSlotToPick.forEach(numInArray));
if (armourPick == 1) {
armourSlotPicked.push(armourSlotToPick[0]);
armourSlotToPick.splice(0,1);
} else if (armourPick == 2) {
armourSlotPicked.push(armourSlotToPick[1]);
armourSlotToPick.splice(1,1);
} else if (armourPick == 3) {
armourSlotPicked.push(armourSlotToPick[2]);
armourSlotToPick.splice(2,1);
} else {
alert("Invalid choice, you suck");
break;
}
armourLoop++;
}
}
I know it probably wouldn't be possible to do the whole return in numInArray() to the prompt, but it shows some working.
Now the problem: I got it working so that each item in the array was numbered (var armourSlotToPick = ["1. Head", "2. Chest", "3. Legs"],) but as you could see, if the player chose 2, then the next time it would show "1. Head (new line) 3. Legs" and when the player chooses 3, a problem would occur, as they were really meant to choose 2. How is it possible to number the items in the array, in a prompt?
I'm possibly over thinking this but I have suffered for a few hours now.
I thank you in advance for any insight you may have,
Daniel.
EDIT: Solved.
Below is the end result, a slight variation from the edited answer from Jonathan Brooks.
var armourSlotToPick = [null, "Head", "Chest", "Legs"]
var armourSlotPicked = [null];
var armourLoop = 1;
function armour() {
while (armourLoop < 4) {
var message = "Pick an armour slot to generate an item for:\n";
for (var i = 0; i < armourSlotToPick.length; i++) {
if (armourSlotToPick[i] !== null) {
message += "" + i + ". " + armourSlotToPick[i] + "\n";
}
}
var armourPick = prompt(message);
if (armourPick > armourSlotToPick.length-1 || armourPick < 1) {
alert("Invalid choice, you suck");
} else {
var insert = armourSlotToPick.splice(armourPick, 1);
armourSlotPicked.push(insert);
}
armourLoop++;
}
armourSlotPicked.splice(0,1);
}
armour();
alert(armourSlotPicked.join("\n"));
I thank all that have contributed to this discussion and the end result, and I hope this is a good example for future problems people may have similar to this.

Check out my fiddle, I think I have a working solution.
What you really want to be using are Object Literals with your own indexing (starting from 1) - if it were me, I would create my own way to iterate over this custom indexing by adding a method to the Object's prototype, but I digress.
You're overcomplicating your code by using a while loop, and that large bulk of if statements is unnecessary: instead, all you need is some basic validation on the input and then you can just trust whatever input passes this validation. That is demonstrated here:
if ( armourPick > armourSlotToPick.length || armourPick < 1 ) {
alert("Invalid choice, you suck");
}
else {
armourSlotPicked.push( armourSlotToPick[armourPick-1] )
alert (armourSlotPicked[armourSlotPicked.length-1].value);
}
Read my code carefully, and you should get a better understanding of how to deal with certain issues.
EDIT:
As per your request, I think I have a solution that suits your needs. Basically all you have to do to have the arrays "start" at an index of 1 is to fill the zeroth element with a null value, like so:
var armourSlotToPick = [null, "Head", "Chest", "Legs"]
var armourSlotPicked = [null];
You just have to remember to take this null object into account in your code, for example:
if (armourSlotToPick[i] !== null) {
message += "" + i + "\n";
}
The indices will update automatically. See this updated fiddle for more details.

use structures / objects as content in the array, instead of just values.
the basic concept:
armourSlotPicked.push({ "key": 1, "value":armourSlotToPick[1]})
alert("value: " + armourSlotPicked[0].value)
alert("key: " + armourSlotPicked[0].key)
edit: responding to comments can take some space.
IMHO a prompt is the completely wrong tool for this, since most browsers would ask the user permission to prevent multiple popups, and since a promt can only return 1 piece of information, you can only ask for 1 thing per popup. Instead you ought to use a div element, with checkboxes for each information..
That being said it can easily be used in a promt.
The prompt is just a built in function, that takes a string as an argument (which is shown as text in the popup) and returns a string with the users input.
what does the magic for you is in fact this:
array.foreach(): The forEach() method executes a provided function once per array element.
in your case that means it calls a function that returns a string for each element in the array, and concatenates the strings.
in the old days you would have written this:
var messageText= "Pick an armour slot to generate an item for:\n"
for(var i = 1; i < armourSlotToPick.length; i++){
messageText += i + ". " + armourSlotToPick[i- 1] + "\n";
}
var armourPick = prompt(messageText);
but in this modern age, you define a printing function, and use it to generate the loop:
function numInArray() {
indexArmour++;
return (indexArmour + ". " + armourSlotToPick[indexArmour - 1] + "\n");
}
//more code before we get to where the function is used....
indexArmour = 0;
var messageText = "Pick an armour slot to generate an item for:\n" + armourSlotToPick.forEach(numInArray);
var armourPick = prompt(messageText);
or in a single line as in your code:
indexArmour = 0; //you forgot this - otherwise the list will only be complete once?
var armourPick = prompt("Pick an armour slot to generate an item for:\n" + armourSlotToPick.forEach(numInArray));
It produces the same output, because it does the same thing, its just written very differently!
If the array holds "object literals" instead of simply values, as I suggest, the old fashioned code would look something like this:
function contains(a, value) {
try{
for (var i = 0; i < a.length; i++) {
if (a[i].value == value) {
return true;
}
}
}
catch(err) {
// do nothing
};
return false;
}
and later..
for(var j = 0; j < 4; j++){
for(var i = 0; i < Math.min(armourSlotToPick.length); i++){
if( contains(armourSlotPicked, armourSlotToPick[i- 1]) )
continue;
var messageText = "Generate an item for armour in slot: " + i + "\n"
messageText += armourSlotToPick[i- 1] + "\n";
}
var armourPick = prompt(messageText);
if (armourPick > 0 && armourPick < armourSlotToPick.length) {
armourSlotPicked.push({"key":j, "value":armourSlotToPick[armourPick]);
}
...
}
//now we have an array that holds information about when what was picked..
or something along those lines.. this is bt.w completely untested, it's just for illustration

You want to use the array index to number your items. Since your numbers are one-based and the index is zero-based, you will need to convert between the two when outputting and interpreting the response.
This approach will also allow you to eliminate all but two of the cases in your if-else statement.

Expanding on the split() method in JavaScript

This is something that has been bothering me for a while.
Assume I'm doing this on a line
var result = "Noble warm and pretty darm Caesar.".split(/(\warm)/);
// ["Noble ", "warm", " and pretty ", "darm", " Caesar."]
Would it be possible to extend the split method in order to manipulate regexp catches with a function like replace does on strings?
Pseudo-code:
var result = "Noble warm and pretty darm Caesar.".split(/(\warm)/, function (match) {
return '<span style="color:red;">' + match + '</span>';
});
// ["Noble ", "<span style=\"color:red;\">warm</span>", " and pretty ", "<span style=\"color:red;\">darm</span>", " Caesar."]

You can define your own function in the prototype object property of the String object.
The following function is an example of what you could do :
String.prototype.splitReplace = function(pattern, fn)
{
var array = this.split(pattern);
for (var i = 0; i < array.length; i++)
{
if (i % 2 == 1)
{
array[i] = fn(array[i]);
}
}
return array;
}
As stated above, this function is just a quick example, to show how you could add a function to the String prototype property. But you should use the smart and robust function declaration #User2121315 gave us in the comments

How to optimize jquery grep method on 30k records array

Is it possible to optimize this code? I have very low performance on this keyup event.
$('#opis').keyup(function () {
if ($('#opis').val() != "") {
var search = $.grep(
svgs, function (value) {
reg = new RegExp('^' + $('#opis').val(), 'i');
return value.match(reg) == null;
}, true);
$('#file_list').html("");
var tohtml = "";
$cnt = 0;
for (var i = 0; i < search.length; i++) {
if ($cnt <= 30) {
tohtml += "<li class='file_item'><a href='' class='preview'>" + search[i] + "</a> <a href='" + search[i] + "' class='print_file'><img src='img/add16px.png' alt='dodaj'/></li></a>";
$cnt++;
} else {
break;
}
}
$('#file_list').html(tohtml);
$(".preview").click(function () {
$('#file_preview').html('<embed src="opisy/' + $(this).html() + '" type="image/svg+xml" pluginspage="http://www.adobe.com/svg/viewer/install/" /> ');
$(".preview").parent().removeClass("selected");
$(this).parent().addClass("selected");
return false;
});
$(".print_file").click(function () {
if (jQuery.inArray($(this).attr('href'), prints) == -1) {
$('#print_list').append('<li>' + $(this).attr('href') + '</li>');
prints.push($(this).attr('href'));
} else {
alert("Plik znajduje się już na liście do wydruku!");
}
return false;
});
} else {
$('#file_list').html(" ");
}
});

var opis = $('#opis')[0]; // this line can go outside of keyup
var search = [];
var re = new RegExp('^' + opis.value, 'i');
for (var i = 0, len = svgs.length; i < len; i++) {
if (re.test(svgs[i])) {
search.push(svgs[i]);
}
}
It's up to 100x faster in Google Chrome, 60x in IE 6.

first thing you have to learn:
$('#opis').keyup(function() {
$this = $(this);
if($this.val()!=""){
// so *$this* instead of *$('#opis')*
// because you are reperforming a *getElementById("opis")* and you've already called it when you used the keyup method.
// and use $this instead of $(this) | pretty much the same problem
so about the grep function, maybe if you cache the results it would help in further searchs I guess, but I don't know if can help you with that

Well the thing with javascript is that it executes under the users environment and not the servers environment so optimization always varies, with large large arrays that need extensive work done on them to I would prefer to handle this server side.
Have you thought about serializing the data and passing them over to your server side, which would handle all the data calculations / modifications and return the prepared result back as the response.
You may also want to take alook at SE:Code Review for more optimization advise.
Some optimization, tips:
if($('#opis').val()!=""){ should be using '!=='.
return value.match(reg)==null; should be ===.
for(var i=0;i<search.length;i++){
reg = new RegExp(...); should be var reg ... as its not defined outside the function as a global.
Move all your variable declarations to the top of the function such as
var i,cnt,search,tohtml etc
i would advise you to start using Google Chrome, it has a built in system for memeory tracking on perticular tabs, you can go to the url about:memory in chrome, which would produce a result like so:
Image taken from: http://malektips.com/google-chrome-memory-usage.html

Each time you perform the grep, you are calling the 'matching' function once per array entry.
The matching function creates a RegExp object and then uses it to perform the match.
There are two ways you could improve this:
Create the RegExp once, outside of the function, and then use a closure to capture it inside the function, so that you don't have to keep recreating the object over and over.
It looks like all you're trying to do is to perform a case-insensitive tests to see whether the sought string is the start of a member of your array. It may be faster to do this more explicitly, using .toUpper and substring. However, that's a guess and you should test to find out.

Way to check a bunch of parameters if they are set or not in JavaScript

So, this happens to me quite frequently, but here's my latest one:
var generic_error = function(title,msg){
if(!title){ title= 'Oops!'; }
if(!msg) { msg = 'Something must have gone wrong, but no worries we\'re working on it!'; }
$.fancybox(
{
content:'\
<div class="error_alert">\
<h2>'+title+'</h2>\
<p>'+msg+'\
</div>'
});
}
Is there a cleaner way to check all params like title and msg above and OR set them as optional OR define defaults in the function like how PHP does it for example? Sometimes i could have 10 options and if(!var){var='defaults'} x 10 is icky...

Slightly shorter but equivalent to what you're doing now is to use "||" AKA "or" AKA "the default operator".
title = title || 'Oops!';
msg = msg || 'Something must have gone wrong, but no worries we\'re working on it!';

I doubt you'll find anything considerably shorter and simpler than if(!title)title='DefaultTitle' for function arguments.
However, I'd even use the longer form to make it more explicit: if (title===null) title='DefaultTitle'.
Here is a related question with an answer, but I think it would just makes your code more complicated. How can I access local scope dynamically in javascript?

You could use ternary notation as recommended by this article but in a simpler form:
var n = null;
!title ? title = 'Oops' : n;
You've also got the arguments[] array which holds the arguments and could be used in a loop, something like this:
function test(one,two,three) {
i=0;
while(typeof(arguments[i]) != 'undefined') {
alert(arguments[i++]);
}
}
test(40,27,399);

switch (arguments.length) {
case 0: title = 'Oops';
case 1: message = 'Something must have gone wrong...';
}

Here's another approach. The argsOK function is a little complex, but calling it is easy.
//-----------------------------------------------------
/*
PURPOSE Ensures a function received all required arguments, no extra
arguments & (if so specified) no arguments are empty.
RETURNS True if the arguments validate, else false.
*/
function argsOk(
functionCallee , // Caller's callee object
allArgsRequired , // True = All arguments are required
emptyArgsAllowed // True = Empty arguments are allowed
){
var ok = true;
for (var i = 0; i < 1; ++i) {
var functionName = functionCallee.toString().split(' ')[1].split('(')[0];
var args = functionCallee.arguments;
var expectedArgCount = functionCallee.length;
var actualArgCount = args.length;
if ((allArgsRequired && actualArgCount < expectedArgCount) ||
(actualArgCount > expectedArgCount)) {
error("Function " + functionName + " expected " + expectedArgCount + " arguments, but received " + actualArgCount + ".");
ok = false;
break;
}
if (emptyArgsAllowed) {
break;
}
for (var j = 0; j < args.length; ++j) {
if (args[j] != null && args[j].length == 0) {
error("Function " + functionName + "() received an empty argument.");
ok = false;
break;
}
}
}
return ok;
}
Example of calling it (a one-liner, as you can see):
//------------------------------------------------
function image(item, name, better)
// PURPOSE Write a request for picture or photo
// ENTRY Init() has been called
{
if (!showingShortVersion()) {
var betterString = '';
if (better != null && better == true)
betterString = 'better ';
if (argsOk(arguments.callee, true, false))
write('<p class="request maintain">If you have ac­cess to a ' + betterString + item + ' of ' + name + ' that we could put on­line, please click here.</p>');
}
}

In general, especially in Javascript, clean != short.
Do not use if(!title){ title= 'Oops!'; } as a general solution, because e.g. 0 and empty string are falsy, too. Arguments that are not set, are undefined, so I prefer using
if (title === undefined) {
title= 'Oops!';
}
It may be more wordy to do so, but It will prevent unwanted side effects, and in my experience, Javascript generates a lot of unwanted side effects, if you try to use shortcuts.