JSON files are compromised of a series of key's and values. I know the potential key's in a given JSON, but not whether or not they have corresponding non-empty values. I have loaded the JSON file into an object called JSON. I want to find the first of several possible key's with a value and then assign that value to a variable. When I say "first" I mean "first" according to a priority list that is not related to the structure of the JSON:
I could do the following and it works:
if(json.age)
myValue = json.age;
else if(json.classYear)
myValue = json.classYear;
else if(json.seniority)
myValue = json.seniority
else
myValue = false;
This works but sucks for several reasons:
It is slow to write
It is annoying to rewrite the key value name each twice in each row
It is a little hard to read
It is very difficult to reason with programatically. I don't have a use case that requires this, but I can imagine wanting to arbitrarily change the order of priority from within my code.
While not terribly slow to process, I can imagine that some other approach may compute faster.
These reasons lead me to believe that the method listed above is not ideal. Is there some other pattern that would be better?
(Note: I recognize that this question borders on a "how best to" as opposed to "how to" phrasing. I know SO is not wild about that sort of question and I don't mean my question to be interpreted as such. Rather, my question should be interpreted as asking, "is there some design pattern that is particularly suited for the problem describe above?)
(Note: I will only accept a vanilla answer, but feel free to provide other answers if you believe they will be helpful).
You could use short-circuit evaluation. You'll still have to write out all of the property names, but I'm not sure there's a way to accomplish this task without doing that.
const myValue = json.age || json.classYear || json.senority || false;
Okay, so if you have a one-dimensional hash table and an array for the priority of keys, then you can use an algorithm like this to select the first one available:
function grab(hash, keyPriority) {
var value;
keyPriority.some(function (key) {
if (hash.hasOwnProperty(key)) { // check if the property exists
value = hash[key];
return true; // break out of loop
}
});
return value;
}
usage:
grab({ c: 3, d: 4 }, ['a', 'b', 'c', 'd']) // 3
You can modify this to work by truthy values, or undefined/null by changing hash.hasOwnProperty(key) to hash[key] or hash[key] != null respectively.
If you are fine with using a bit of JQuery then the following code snippet should do the job I guess.
$.each(JSONObj, function(key, value){
if (!(value === "" || value === null)){
myValue = value;
return false; //to break the loop once a valid value is found
}
});
This will assign the first valid value to your variable myValue and will also exit the loop once a valid value is found.
Related
Example:
When I check a variable containing this value [""] it returns false.
var th=[]
th.push("");
if($("#multiselect").val()==th)
It returns always false.
Thank you.
Edit 1:
changed Var to var. It was a typo.
Edit 2:
Actually, the problem I faced was I was trying to get the value from a multi-select input. The multi-select input sometimes returns values as [""] even I haven't selected any values basically it's a plugin. So I was confused and I thought [""] is a fixed primitive value like 1, 10, "bla blah",.. So I tried to compare it with the same array as the right-hand side of the '=' operator.
It was stupid. Now I posted the solution to my problem and I explained my stupidity.
there are two things:
Change Var to var
You can use includes method of Array as:
var th = [] <==== chnage Var to var
th.push("");
if(th.includes($("#multiselect").val())) { <=== you can use includes method of array
// DO whatever you want
}
Make sure var is lowercased.
You are accessing th as an array, so you’ll need to specify the index of the value you are checking: th[0]
Use triple equals, too: .val()===th[0]
Double check the jquery docs if you’re still running into trouble.
Happy coding!
A couple of things to consider:
You have a typo in the code above; var is valid; Var is invalid.
Browser will aptly complain to solve this typo.
You are comparing an array to DOM value; this will always be false.
DOM is a costly process. Unless the value associated is dynamic, its better to read once, store value into a variable and continue processing instead of reading from DOM always.
You could choose to try something on these lines:
let arr = [1,2,3,4];
let domValue = $("#multiselect").val();
arr.push(5);
arr.map((el, ix) => {
if el === domValue return true; //or choose to do something else here.
});
var th=[]; //It is var not Var
th.push("");
if($("#multiselect").val()==th[0]) // change th to th[0]
I am unable to comment so having to use an answer for now. Are you trying to check if an array has any values? If so you can use
if(th.length){
// do something
}
If you want to check a normal variable for empty string you can simply use
if(th == “”){
//do something
}
I found the solution after a couple of days when I posted this question. Now I can feel how stupid this question was.
Anyway, I'm answering this question so it might help others.
Answer to my question:
When two non-primitive datatype objects(which is the Array here) are compared using an assignment operator, it compares its reference of the object. So the object creation of both arrays would be different. If I want to check the array has [""] value, I should do something like the below.
function isArrValEmptyCheck(value) {
return !value || !(value instanceof Array) || value.length == 0 || value.length == 1 && value[0] == '';
}
console.log(isArrValEmptyCheck([""]));//returns true
console.log(isArrValEmptyCheck(["value1"]));//returns false
Sorry for the late response. Thanks to everyone who tried to help me.
I'm only sharing a small bit of code because there is so much going on, and I hope this is enough to answer my question.
I have some existing JS where a value is determined with an OR statement and I think I need to convert that to an IF statement. The final output is currently giving me both values if they both exist, and I only want "question" where both "question" and "name" values exist.
var question = new fq.Question(questionData.answerId, topicId,
questionData['question'] || questionData['name'],
questionData['text']);
Instead of using the OR operator (answerData['question'] || answerData['name']), I'd like to do something similar to the following:
if (questionData['question'] is undefined) {
use questionData['question'];
} else {
use instead questionData['name']
}
But, I don't know how I might accomplish such a statement within the () in the existing code pasted above. The name variable/value is always present, so there's no risk in defaulting to that. Question is only defined some of the time. And I don't ever want both appearing.
This is probably outside of the scope of my query here, but to fill in a little more detail, this code eventually outputs JSON files for topics and questions. Topics only have names values, and questions have both names and questions, but I only want the questions json to include questions values, not names. I'm pretty sure this is the key part in all of the JS to determin
Create a function and get value from there.
Need to remember scope of function:
Example Snippet:
var that = this;
var question = new fq.Question(questionData.answerId, topicId,
that.getValue(),
questionData['text']);
function getValue() {
if (questionData['question']) { //null and undefined both are false
return questionData['question']
} else {
return questionData['name']
}
}
I have an array that keep changing with the user input.
for example:
user = ['a','b',['c','d'],'e',['f','g',['h','i'],'j']]
I also have a pointer to point where to make a change.
pointer = [1] change value at user[1]
pointer = [2,1] change value at user[2][1]
pointer = [4,2,2] change value at user[4][2][2]
Dimension is mostly not the same and can be more than 10.
Now I'm making a string then eval.
Can I write a function without using eval?
Use lodash's _.set!
_.set(user, [4,2,1], '!')
Or, if you don't want lodash, you can implement this one yourself.
function setDeep(obj, path, val) {
if (path.length === 1)
obj[path[0]] = val;
else
setDeep(obj[path.shift()], path, val)
}
// then use: setDeep(user, [4,2,1], 'something').
Note that this version will throw if the specified key doesn't exist. This is also not a good example of clarity and maintainability, so you'll need to improve it, but it's a good starting point - it does what you want.
If you neet to get instead of set - use lodash's _.get or implement it yourself, it would be very similar to my setDeep.
I assume that the user's input is a string and not an array like in your example, because you mentioned eval, otherwise it's a completely different approach.
var user = "['a','b',[4,'d'],'e',['f','g',['h','i'],'j']]";
JSON.parse(user.replace(/'/g, "\""));
In Javascript what is the best way to handle scenarios when you have a set of arrays to perform tasks on sets of data and sometimes you do not want to include all of the arrays but instead a combination.
My arrays are labeled in this small snippet L,C,H,V,B,A,S and to put things into perspective the code is around 2500 lines like this. (I have removed code notes from this post)
if(C[0].length>0){
L=L[1].concat(+(MIN.apply(this,L[0])).toFixed(7));
C=C[1].concat(C[0][0]);
H=H[1].concat(+(MAX.apply(this,H[0])).toFixed(7));
V=V[1].concat((V[0].reduce(function(a,b){return a+b}))/(V[0].length));
B=B[1].concat((MAX.apply(this,B[0])-MIN.apply(this,B[0]))/2);
A=A[1].concat((MAX.apply(this,A[0])-MIN.apply(this,A[0]))/2);
D=D[1].concat((D[0].reduce(function(a,b){return a+b}))/(D[0].length));
S=S[1].concat((S[0].reduce(function(a,b){return a+b}))/(S[0].length));
}
It would seem counter-productive in this case to litter the code with tones of bool conditions asking on each loop or code section if an array was included in the task and even more silly to ask inside each loop iteration with say an inline condition as these would also slow down the processing and also make the code look like a maze or rabbit hole.
Is there a logical method / library to ignore instruction or skip if an option was set to false
All I have come up with so far is kind of pointless inline thing
var op=[0,1,1,0,0,0,0,0]; //options
var L=[],C=[],H=[],V=[],B=[],A=[],D=[],S=[];
op[0]&&[L[0]=1];
op[1]&&[C[0]=1,console.log('test, do more than one thing')];
op[2]&&[H[0]=1];
op[3]&&[V[0]=1];
op[4]&&[B[0]=1];
op[5]&&[A[0]=1];
op[6]&&[A[0]=1];
It works in that it sets only C[0] and H[0] to 1 as the options require, but it fails as it needs to ask seven questions per iteration of a loop as it may be done inside a loop. Rather than make seven versions of the the loop or code section, and rather than asking questions inside each loop is there another style / method?
I have also noticed that if I create an array then at some point make it equal to NaN rather than undefined or null the console does not complain
var L=[],C=[],H=[],V=[],B=[],A=[],D=[],S=[];
L=NaN;
L[0]=1;
//1
console.log(L); //NaN
L=undefined;
L[0]=1
//TypeError: Cannot set property '0' of undefined
L=null
L[0]=1
//TypeError: Cannot set property '0' of null
Am I getting warmer? I would assume that if I performed some math on L[0] when isNaN(L)===true that the math is being done but not stored so the line isn't being ignored really..
If I understand what you want I would do something like this.
var op = [...],
opchoice = {
//these can return nothing, no operation, or a new value.
'true': function(val){ /*operation do if true*/ },
'false': function(val){ /*operation do if false*/ },
//add more operations here.
//keys must be strings, or transformed into strings with operation method.
operation: function(val){
//make the boolean a string key.
return this[''+(val == 'something')](val);
}
};
var endop = [];//need this to prevent infinite recursion(loop).
var val;
while(val = op.shift()){
//a queue operation.
endop.push(opchoice.operation(val));
}
I'm sure this is not exactly what you want, but it's close to fulfilling the want of not having a ton of conditions every where.
Your other option is on every line do this.
A = isNaN(A) ? A.concat(...) : A;
Personally I prefer the other method.
It looks like you repeat many of the operations. These operations should be functions so at least you do not redefine the same function over and over again (it is also an optimization to do so).
function get_min(x)
{
return +(MIN.apply(this, a[0])).toFixed(7);
}
function get_max(x)
{
return +(MAX.apply(this, a[0])).toFixed(7);
}
function get_average(x)
{
return (x[0].reduce(function(a, b) {return a + b})) / (x[0].length);
}
function get_mean(x)
{
return (MAX.apply(this, x[0]) - MIN.apply(this, x[0])) / 2;
}
if(C[0].length > 0)
{
L = L[1].concat(get_min(L));
C = C[1].concat(C[0][0]);
H = H[1].concat(get_max(H));
V = V[1].concat(get_average(V));
B = B[1].concat(get_mean(B));
A = A[1].concat(get_mean(A);
D = D[1].concat(get_average(D));
S = S[1].concat(get_average(S));
}
You could also define an object with prototype functions, but it is not clear whether it would be useful (outside of putting those functions in a namespace).
In regard to the idea/concept of having a test, what you've found is probably the best way in JavaScript.
op[0] && S = S[1].concat(get_average(S));
And if you want to apply multiple operators when op[0] is true, use parenthesis and commas:
op[3] && (V = V[1].concat(get_average(V)),
B = B[1].concat(get_mean(B)),
A = A[1].concat(get_mean(A));
op[0] && (D = D[1].concat(get_average(D)),
S = S[1].concat(get_average(S)));
However, this is not any clearer, to a programmer, than an if() block as shown in your question. (Actually, many programmers may have to read it 2 or 3 times before getting it.)
Yet, there is another solution which is to use another function layer. In that last example, you would do something like this:
function VBA()
{
V = V[1].concat(get_average(V));
B = B[1].concat(get_mean(B));
A = A[1].concat(get_mean(A));
}
function DS()
{
D = D[1].concat(get_average(D));
S = S[1].concat(get_average(S));
}
op = [DS,null,null,VBA,null,null,...];
for(key in op)
{
// optional: if(op[key].hasOwnProperty(key)) ... -- verify that we defined that key
if(op[key])
{
op[key](); // call function
}
}
So in other words you have an array of functions and can use a for() loop to go through the various items and if defined, call the function.
All of that will very much depend on the number of combinations you have. You mentioned 2,500 lines of code, but the number of permutations may be such that writing it one way or the other will possibly not reduce the total number of lines, but it will make it easier to maintain because many lines are moved to much smaller code snippet making the overall program easier to understand.
P.S. To make it easier to read and debug later, I strongly suggest you put more spaces everywhere, as shown above. If you want to save space, use a compressor (minimizer), Google or Yahoo! both have one that do a really good job. No need to write your code pre-compressed.
My intention is to get your thoughts and criticism about the script below, as regards the algorithm's design, performance and cross-browser compatibility.
I have just started getting into JavaScript having missed out on its awesomeness for quite a while. My background and experience is in developing C/C++/PHP based RESTful backends.
In order to understand the language and the right way of using it, I decided to do something which I am sure has been done many times before. But learning to use a new language and paradigm often entails pain anyway.
This is my attempt to create a normal form processing and validation script/ function.
In order to reduce complexity and keep code simple/clean, I decided to use HTML5 Custom Data Attributes (data-*) to assign metadata for each element in the form:
Data-Required: True or False. If set to true, this parameter makes the form-field required and so it cannot be empty. A value set to false indicates that the field is optional. Default is false.>
Data-Type: Type of validation to be performed. Examples include 'email', 'password', 'numbers' or any other 'regexp'.
A fairy simple example of such a form would be:
<form action="postlistings" id="postlistings" enctype='multipart/form-data' method="post" class="postlistings">
<ul class="login-li">
<li>
<input class="title" name="title" type="title" id="title" data-required="true" data-type="title"></a>
</li>
<li>
<textarea name="body" id="elm1" class="elm1" name="elm1" data-type="body" data-required="true" >
</textarea>
</li>
<li>
<span class="nav-btn-question">Add Listing</span>
</li>
</ul>
</form>
Reminder: This is my first piece of JavaScript code.
The idea is to call Form while passing the form name to retrieve and validate all the field values in one loop for performance. The validation involves two steps as can be guessed from the Data-* attributes described above:
i. Check for required form fields.
In case the values fail to meet step 1 requirement, an error message from configuration is pulled for the specific form value. Thus, for all values that fail to meet this requirement, an array of error messages are collected and passed on to the View.
ii. Perform respective validations.
Validations are only performed if all the values passed step 1. Otherwise, they follow the same steps as indicated in 1 above.
function Form(){
var args = Array.prototype.slice.call(arguments),
formName = args[0],
callback = args.pop(),
userError = [{type: {}, param: {}}],
requiredDataParam = 'required',
typeDataParam = 'type',
form = document.forms[formName],
formLength = form.length || null,
formElement = {id: {}, name: {}, value: {}, required: {}, type: {}};
function getFormElements(){
var num = 0;
var emptyContent = false;
for (var i = 0; i < formLength; i += 1) {
var formField = form[i];
formElement.id[i] = inArray('id', formField) ? formField.id : null;
formElement.name[i] = inArray('name', formField) ? formField.name : null;
formElement.value[i] = inArray('value', formField) ? formField.value : null;
formElement.required[i] = getDataAttribute(formField, requiredDataParam);
formElement.type[i] = getDataAttribute(formField, typeDataParam);
if (formElement.required[i] === true){
if(!formElement.type[i]) {
error('Validation rule not defined!');
}
else if (!formElement.value[i]) {
userError[num++] = {'type': 'required', 'param': form[i]};
emptyContent = true;
}
}
if (emptyContent === false) {
// Perform validations only if no empty but required form values were found.
// This is so that we can collect all the empty
// inputs and their corresponding error messages.
}
}
if (userError) {
// Return empty form errors and their corresponding error messages.
}
return formElement;
};
// Removed the getFormParam function that was not used at all.
return {
getFormElements: getFormElements
}
};
Two outside functions that are used in the JS script above (from JQuery source):
var inArray = function(elem, array){
if (array.indexOf){
return array.indexOf(elem);
}
for (var i = 0, length = array.length; i < length; i++){
if (array[i] === elem){
return i;
}
}
return -1;
}
// This is a cross-platform way to retrieve HTML5 custom attributes.
// Source: JQuery
var getDataAttribute = function(elem, key, data) {
if (data === undefined && elem.nodeType === 1) {
data = elem.getAttribute("data-" + key);
if (typeof data === "string") {
data = data === "true" ? true :
data === "false" ? false :
data === "null" ? null :
!CheckType.isNaN ? parseFloat(data) :
CheckType.rbrace.test(data) ? parseJSON(data) :
data;
}
else {
data = undefined;
}
}
return data;
}
An example of Config Error messages can be set as follows:
var errorMsgs = {
ERROR_email: "Please enter a valid email address.",
ERROR_password: "Your password must be at least 6 characters long. Please try another",
ERROR_user_exists: "The requested email address already exists. Please try again."
};
As I post this for your review, please ignore any styling conventions that I might not have followed. My intention is to get your expert reviews on anything I should be doing different or could do better concerning the code itself, and the algorithm.
Besides the styling conventions, all criticism and questions are welcome.
First I'd like to clear up a common misconception. Forgive me if you already understand this clearly; maybe it will be helpful for someone else.
Learning and using jQuery or a similar library does not preclude or conflict with learning the JavaScript language. jQuery is simply a DOM manipulation library which takes away many of the pain points of using the DOM. There's plenty of room to learn and use JavaScript, the language, even if you use a library to abstract away some of the DOM details.
In fact, I would argue that using the DOM directly is likely to teach bad JavaScript coding habits, because the DOM is very much not a "JavaScript-ish" API. It was designed to work identically in JavaScript and Java and potentially other languages, and so it completely fails to make good use of the features of the JavaScript language.
Of course as you said, you're using this as a learning exercise; I just don't want you to fall into the trap that I've seen many people fall into of thinking, "I don't want to learn jQuery, because I want to learn JavaScript instead!" That's a false dichotomy: you have to learn JavaScript in either case, and using jQuery for the DOM doesn't interfere with that at all.
Now some details...
While it's OK to quote property names in an object literal and when you reference the properties, it's customary - and more readable - not to quote them when they are valid JavaScript names. e.g. in your formElement object
formElement = { id: {}, name: {}, value: {}, required: {}, type: {} };
(there was a missing semicolon at the end there too)
and where you use the names you can do:
formElement.id[i] = ...
formElement.name[i] = ...
etc.
Don't run your loops backwards unless the program logic requires it. It doesn't make the code faster except possibly in the case of an extremely tight loop, and it makes it unclear whether you're just prematurely optimizing or actually need the backwards loop.
Speaking of optimization, that loop has several inArray() calls. Since each of those loops through an array, that could be more of a performance impact than the outer loop. I imagine these arrays are probably pretty short? So performance wouldn't matter at all anyway, but this is something to think about in cases where you have longer arrays and objects. In some cases you can use an object with property names and values for a faster lookup - but I didn't look closely enough at what you're doing to suggest anything.
In any case, you're using inArray() wrong! But not your fault, that is a ridiculously named function in jQuery. The name clearly suggests a boolean return value, but the function returns the zero-based array index or -1 if the value is not found. I strongly recommend renaming this function as indexOf() to match the native Array method, or arrayIndex(), or some such.
That same loop has form[i] repeated numerous times. You could do this at the top of the loop:
var field = form[i];
and then use field throughout, e.g. field.id instead of form[i].id. This is generally faster, if it matters (which it probably doesn't here), but more importantly it's easier to read.
Do not use strict boolean comparisons like if( foo === true ) and if( bar === false) unless you really need to - and those cases are rare. The code sends a signal to the reader that there is something going on that's different from the usual boolean test. The only time these particular tests should be used is when you have a variable that may contain a boolean value or may contain some other type of value, and you need to distinguish which is which.
A good example of a case where you should use tests like these is an optional parameter that defaults to true:
// Do stuff unless 'really' is explicitly set to false, e.g.
// stuff(1) will do stuff with 1, but stuff(1,false) won't.
function stuff( value, really ) {
if( really === false ) {
// don't do stuff
}
else {
// do stuff
}
}
That specific example doesn't make a lot of sense, but it should give you the idea.
Similarly, an === true test could be used in a case where need to distinguish an actual boolean true value from some other "truthy" value. Indeed, it looks like this line is a valid case for that:
if (formElement['required'][i] === true){
given that if (formElement['required'][i] comes from the getDataAttribute() function which may return a boolean or other type.
If you are just testing for truthiness, though - and this should be most of the time - simply use if( foo ) or if( ! foo ). Or similarly in a conditional expression: foo ? x : y or !foo ? x : y.
The above was a long-winded way of saying that you should change this:
if (empty_content === false) {
to:
if (!empty_content) {
Your getFormParam() function goes to some work to convert an undefined result to null. There is usually no reason to do this. I don't see any place where that function is called, so I can't advise specifically, but in general you'd be testing for truthiness on something like this, so null and undefined would both be treated as false. Or in cases where you do need to distinguish null/undefined from other values (say, an explicit false), you can easily do it with != null or == null. This is one case where the "looser" comparison performed by == and != is very useful: both null and undefined evaluate the same with these operators.
You asked to ignore coding style, but one little suggestion here: You have a mix of camelCaseNames and names_with_underscores. In JavaScript, camelCaseNames are more idiomatic for function and variable names, with PascalCaseNames for constructor functions. Of course feel free to use underscores where they make more sense, for example if you're writing code that works with database columns in that format you may want your variable names to match the column names.
Hope that helps! Keep up the good work.
Update for your new code
I'm having a bit of trouble following the logic in the code, and I think I know part of the reason. It's a combination of naming conventions and inside-out objects.
First, the name formElement is really confusing. When I see element in JavaScript, I think of either a DOM element (HTMLElement) or an array element. I'm not sure if this formElement represents one or the other or neither.
So I look at the code to figure out what it's doing, and I see it has id:{}, name:{}, ... properties, but the code later treats each of those as an Array and not an Object:
formElement.id[i] = ...
formElement.name[i] = ...
formElement.value[i] = ...
formElement.required[i] = ...
formElement.type[i] = ...
(where i is an integer index)
If that code is right, those should be arrays instead: id:[], name:[], ....
But this is a red flag. When you see yourself creating parallel arrays in JavaScript, you're probably doing it wrong. In most cases you're better off replacing the parallel arrays with a single array of objects. Each of the objects in that array represents a single slice through all your parallel arrays, with a property for each of the previous arrays.
So, this object (where I've made the correction from {} to [] to match its current use):
formElement = { id: [], name: [], value: [], required: [], type: [] };
should be:
formInfo = [];
and then where you have the code that goes:
formElement.id[i] = ...;
formElement.name[i] = ...;
formElement.value[i] = ...;
formElement.required[i] = ...;
formElement.type[i] = ...;
It should be:
var info = {
id: ...,
name: ...,
value: ...,
required: ...,
type: ...
};
formInfo.push( info );
and adjust the rest of the code to suit. For example:
formElement.required[i]
would be:
formInfo[i].required
or even simpler since it's in the same function:
info.required
And note: I'm not saying info and formInfo are great names :-) they are just placeholders so you can think of a better name. The main idea is to create an array of objects instead of a set of parallel arrays.
One last thing and then I'm out of time for now.
That getDataAttribute() function is a complicated little piece of work. You don't need it! It would be simpler would just call the underlying function directly where you need it:
var info = {
...
required: formField.getAttribute('data-required') === 'true',
type: formField.getAttribute('data-type')
};
This also gives you full control of how the attributes are interpreted - as in the === 'true' test above. (This gives you a proper boolean value, so when you test the value later you don't have to use === true on it.)
On a stylistic note, yes, I did hard code the two 'data-xxxx' names right there, and I think that's a better and more clear way to do it.. Don't let your C experience throw you off here. There's no advantage to defining a string "constant" in this particular case, unless it's something that you want to make configurable, which this isn't.
Also, even if you do make a string constant, there's a minor advantage to having the complete 'data-whatever' string instead of just 'whatever'. The reason is that when somebody reads your HTML code, they may see a string in it and search the JS code for that string. But when they search for data-whatever they won't find it if the data- prefix is automagically prepended in the JS code.
Oh, I forgot one last thing. This code:
function Form(){
var args = Array.prototype.slice.call(arguments),
formName = args[0],
callback = args.pop(),
is working way too hard! Just do this instead:
function Form( formName, callback ) {
(and keep the var for the remaining variable declarations of course)
I cannot add comments yet so here is a little tip. I would separate the getFormElements() into smaller private functions. And I would add the errorMsgs to the Form function.
But for a first script in JavaScript, it is very impressive. This is actually the real reason I respond. I think it deserves more upvotes, and I would be very interested in a JS ninja responding to this question.
Good luck!