I want to create an object that can parse a certain filetype. I've looked at some of the files in the File API and I want my object to work about the same. So basically, what I want is this:
A function, called CustomFileParser. I want to be able to use it as the following:
var customFileParser = new CustomFileParser();
customFileParser.parsed = paresed;
customFileParser.progress = progress;
customFileParser.parse(file);
function parsed(event){
//The file is loaded, you can do stuff with it here.
}
function progess(event){
//The file load has progressed, you can do stuff with it here.
}
So I was thinking on how to define this object, but I'm not sure how to define these events and how I should do this.
function customFileParser(){
this.parse = function(){
//Do stuff here and trigger event when it's done...
}
}
However, I'm not sure how to define these events, and how I can do this. Anyone can give me a hand?
Javscript is prototype-based OOP language, not class-based like most other popular languages. Therefore, the OOP constructs are a bit different from what you might be used to. You should ignore most websites that try to implement class-based inheritance in JS, since that's not how the language is meant to be used.
The reason people are doing it because they are used to the class-based system and are usually not even aware that are alternatives to that, so instead of trying to learn the correct way, they try to implement the way that they are more familiar with, which usually results in loads and loads of hacks or external libraries that are essentially unnecessary.
Just use the prototype.
function CustomFileParser(onParsed, onProgress) {
// constructor
this.onParsed = onParsed;
this.onProgress = onProgress;
};
CustomFileParser.prototype.parse = function(file) {
// parse the file here
var event = { foo: 'bar' };
this.onProgress(event);
// finish parsing
this.onParsed(event);
};
And you can use it like so
function parsed(event) {
alert(event);
}
function progress(event) {
alert(event);
}
var customFileParser = new CustomFileParser(parsed, progress);
var file = ''; // pseudo-file
customFileParser.parse(file);
From what it sounds to me i think you need your program to look like this
function customFileParser( onparse , progress){
this.onparse = onparse;
this.progressStatus = 0;
this.progress = progress;
this.parser = function (chunk)
}
this.parse = function(){
// Do stuff of parsing
// Determine how much data is it
// Now make a function that parses a bit of data in every run
// Keep on calling the function till the data is getting parsed
// THat function should also increase the percentage it think this can be done via setTimeout.
// After every run of the semi parser function call the progress via something like
this.parser();
if(progressStatus <100){
this.progress(this.progressStatus);
}else{
this.parsed();
}
}
}
and u can create instance of that object like
var dark = new customFileParser( function () { // this tells what to
do what parsed is complete } , function (status) { // this tells what
to do with the progress status } ) ;
using the method i suggested. you can actually define different methods for all the instances of the object you have !
Related
Edit: the code below was made up on the spot to show how I was going about what I was doing. It definietely won't run, it is missing a lot of things.
Here is a working example in codepen: https://codepen.io/goducks/pen/XvgpYW
much shorter example: https://codepen.io/goducks/pen/ymXMyB
When creating a function that is using call or apply, the this value stays null when using getPerson. however, when I use apply or call with getPerson it returns the correct person.
Please critique, I am really starting to learn more and more. I am in the middle of a project section so it might be hard to change all the code, but my next project could implement this better.
call and apply are setting to the window and not the object.
I will provide code that is much simpler with the same concept of what I am talking about.
function createPerson(){
this.manager = null;
this.teamManager = null;
this.setTeamManager = function(val){
this.teamManager = val;
}
this.setManager = function(val){
console.log('setting manager to',val);
this.teamManager = val;
}
this.getTeamManager = function(){
console.log('setting team manager to',val);
return this.teamManager ;
}
this.getManager = function(){
return this.manager;
}
this.appendSelect = function(elem){
var that = this;
createOtherSelects(that,elem);
}
//some functions that create selects with managers etc
//now assume there are other selects that will filter down the teams,
//so we might have a function that creates on change events
function createOtherSelects(that){
//code that creates locations, depending on location chosen will
//filter the managers
$('#location').on('change',function(){
//do some stuff
//... then call create management
createManagement(that,elem);
});
}
function createManagement(that,elem){
var currentLocation = that.location; //works
var area = that.area;//works ... assume these are set above
//code that returns a filter and unique set of managers back
that.teamManager = [...new Set(
data.map(person=>{
if(person.area==area &&
person.currentLocation==currentLocation
){
return person;
}
})
)].filter(d=>{if(d){return d}});
if(elem.length>0){
var selectNames = ['selectManager','selectTeamManager'];
var fcns = [that.setManager,that.setTeamManager];
for(var i = 0; i < selectNames.length;i++){
//do stuff
if(certainCriteriaMet){
// filter items
if(filteredManager == 1){
fcns[i].call(null,currentManager);//
}
}
}
}
}
}
var xx = new createPerson()
In console I see setting manager and setting team manager to with the correct values.
however when I call xx in console, I see everything else set except for
xx.teamManager and xx.manager
instead it is applying to the window, so if I type teamManager in the console, it will return with the correct person.
If I straight up say
that.setManager('Steve')
or even it works just fine.
xx.setManager('steve')
the this value in setManager is somehow changing from the current instance of the object to this window. I don't know why, and I would like to learn how to use apply and call using that for future reference.
I think the issue is with your following code
fcns[i].call(null,currentManager)
If you are not supplying "this" to call, it will be replaced with global object in non-strict mode.
fcns[i].call(that,currentManager)
See mdn article here
From your codepen example, you need to change that line
fcnset[0].apply(that,[randomName]);
The first argument of the apply method is the context, if you are not giving it the context of your method it's using the global context be default. That's why you end up mutating the window object, and not the one you want !
I'm a new dev coming from a Ruby background. Recently I've been working very hard in JS and I'm having some issues with class inheritance in the new ES 6. I feel like it may be an issue with my understanding of JS or conflating it to much to Ruby. I've been trying to translate a Ruby Project into JS to practice, but I'm now failing a feature test.
Failing Feature test when trying to initialize two instances of a class
const STATS = { str:1, dex:1, int:1 }
class Example {
constructor(race, clas) {
this.race = race,
this.clas = clas,
this.stats = this.add(STATS)
}
add(stats) {
if(this.race != 'empty'){
stats.str += this.race.str
stats.dex += this.race.dex
stats.int += this.race.int
}
if(this.clas != 'empty') {
stats.str += this.clas.str
stats.dex += this.clas.dex
stats.int += this.clas.int
}
return stats
}
}
var a = new Example({str: 1, dex:0, int:0}, 'empty');
var b = new Example('empty', {str: 0, dex:0, int:1});
console.log('Should be str:2 dex:1 int:1');
console.log(a.stats);
console.log('Should be str:1 dex:1 int:2');
console.log(b.stats);
My class has functions that change the state when constructed, but the issue is any time a new Class is called it retains the changes from the previous variable. It is only an issue on my feature test as it is the only time that class is called twice.
This is the link to my feature test https://github.com/RyanWolfen7/jsRPG/blob/master/cypress/integration/featureTest/characterFeature_test.js
And this is the class thats failing the tests
https://github.com/RyanWolfen7/jsRPG/blob/master/models/characters/character.js
Honestly I'm probably going to scrap my project and start fresh anyways, but I would like to understand what my issue is. I was taking an OOD approach to JS and translating my ruby project https://github.com/RyanWolfen7/ruby_rpg to JS. I'm not sure if its because I wrote the test wrong or a deep misunderstanding of how es-6 works.
Things I have tried:
Creating a new object
Assigning a newly created object to new class
It's not an inheritance issue. In fact, it has nothing to do with OO at all. What you are seeing is the result of the fact that most things in javascript are references (pointers) but you are writing code as if STATS is a value.
In your function add you do this:
add(stats) {
if(this.race != 'empty'){
// modifying passed in object, not creating new object
stats.str += this.race.str
stats.dex += this.race.dex
stats.int += this.race.int
}
if(this.clas != 'empty') {
// modifying passed in object, not creating new object
stats.str += this.clas.str
stats.dex += this.clas.dex
stats.int += this.clas.int
}
return stats
}
So no matter how many times you call add() and from whichever instance of Example you call it from you are only accessing and overwriting the single shared STATS object.
To create new copies of STATS on each function call you need to copy it to a new object. The fastest old-school way to do this is to serialise the object to a string then convert the string back to an object:
add (input) {
var stats = JSON.parse(JSON.stringify(input));
// ...
}
This feels ugly but multiple benchmarks really did show it to be the fastest method.
Modern javascript can do this using Object.assign:
add (input) {
var stats = Object.assign({},input);
// ...
}
However, I don't know if it is faster. You will have to benchmark it yourself. You can google the phrase "js clone object" for more info.
First things first: I'm not sure whether the information that I'm going to provide will be enough, I will happily add additional information if needed.
I'm serializing a complex structure into the JSON-Format, Field[i][0] is the "this"-reference to an object.
Firebug's Output on JSON.Stringify(myObj)
This is all fine and working as long as I keep it all JS. But now I have the requirement to serialize and send it to my backend to get the reference + computed information back.
Now how do I map back to the reference I had before? How do I bind this ref back to an Object?
This $$hash thing looks internal and proprietarish so I havent even bothered trying something like Object[$$hash] = ref or whatever.
This general idea probably seems pretty whack, but the result is returned asynchrously and I need an identifier to bind the new information back to the original object. Obviously I could just make up my own identifier for that, but I was wondering whether there's an option to solve it this way.
EDIT
The objects are created like this (likewise)
var arrayOfObj = []
arrayOfObj.push(new Object.With.SomeSettersAndGetters());
The Object has a method like
function GetRef(){
return this;
}
Which I'm using to keep a ID/Ref through my code.
Thank you!
Update
If you want to update a series of instances and make many Ajax requests, then you need to look at Ajax long polling and queueing techniques. You won't be able to preserve the reference, but regardless of what Ajax technique you use, make use of the below trick to preserve the reference.
Add long polling on top and you're good to go.
The idea is this:
Assume the server will respond in JSON format. If you need to refer to the original references, here's my two cents:
Update the exact references when the server replies. Say you have 10 instances of Something stored in an array. On a successful response, you use the methods in the Something class to update the specific instances in whatever way you want.
/**
* The array with something instances.
* #type {Array.<Something>}
*/
var instances = [];
/**
* The Ajax success function.
* #param {Event} event The event object.
*/
function ajaxSuccess(event) {
var response = event.target.getResponseText();
var actualResponse = JSON.parse(response);
for (var i = 0, len = actualResponse.length; i++) {
instances[i].setWhatever(actualResponse[i].whatever);
};
};
The above is a more procedural approach. If you want full blown OOP in JS, then you think in modular design patterns. Say you have a module that loads data into some place. Basically, everything related to that module is an instance property.
var myModule = function() {
this.whatever = 1;
};
myModule.prototype.loadMore = function() {
var request = new XMLHttpRequest(),
that = this; // store a reference to this.
request.send(); // etc
request.onreadystatechange = that.onSucess;
};
myModule.prototype.onSucess = function(event) {
var response = JSON.parse(event.target.getResponseText());
this.whatever = response.whatever;
};
var moduleInstance = new myModule();
myModule.loadMore();
// Now the scope is always preserved. The callback function will be executed in the right scope.
Let's assume on the backend side of things, you have a model class that mimics your client side JavaScript model. Say you want to update a reference inside a model that displays text. I use Scala on the backend, but look at the fields/properties and ignore the syntax.
case class Article (
title: String,// these are my DB fields for an Article.
punchline: String,
content: String,
author: String
);
// now assume the client is making a request and the server returns the JSON
// for an article. So the reply would be something like:
{"title": "Sample title", "punchline": "whatever", "content": "bla bla bla boring", "author": "Charlie Sheen"};
// when you do
var response = JSON.parse(event.target.getResponseText());
// response will become a JavaScript object with the exact same properties.
// again, my backend choice is irrelevant.
// Now assume I am inside the success function, which gets called in the same scope
// as the original object, so it refers TO THE SAME THING.
// the trick is to maintain the reference with var that = this.
// otherwise the onSuccess function will be called in global scope.
// now because it's pointing to the same object.
// I can update whatever I want.
this.title = response.title;
this.punchline = response.punchline;
this.content = response.content;
this.author = response.author;
// or I can put it all in a single variable.
this.data = response;
What you need to remember is that scope needs to be preserved. That's the trick.
When I do var that = this; I copy a reference to the model instance. The reference is remembered through higher-order, not current scope.
Then I tell the XMLHttpRequest object to call that.ajaxSuccess when it is complete. Because I used that, the ajaxSuccess function will be called in the scope of the current object. So inside the ajaxSuccess function, this will point to the original this, the same instance.
JavaScript remembers it for me it when I write var that = this;
I'm trying to extend the functionality of some methods of the 2dcontext object, however I can't get it to work the way I want: I want to override a method, but I want to call the original method from the overridden method like this:
//First get the original context
var ctx = canvas.getContext("2d");
//Create a class which uses ctx as it's prototype
var ExtendedContext = function (){};
ExtendedContext.prototype = ctx;
//And extend a method
ExtendedContext.prototype.fillRect = function(x, y, width, height) {
//Do some stuff
this.prototype.fillRect(x, y, width, height); //Doesn't work
//Do some more stuff
};
How can I call the original fillRect method from inside my own method?
You can store the reference of the original function just like that:
var oldFillRect = ctx.fillRect;
and then call it like
ExtendedContext.prototype.fillRect = function() {
//Do some stuff
oldFillRect.apply(this, arguments);
//Do some more stuff
};
This technique is sometimes called 'duck punching' or a 'function hook'. In this particular instance, you should also be able to use the Object.getPrototypeOf method to get the original function reference. This would look like
ExtendedContext.prototype.fillRect = function() {
//Do some stuff
Object.getPrototypeOf(ExtendedContext.prototype).fillRect.apply(this, arguments);
//Do some more stuff
};
So you don't even need to store a reference.
No need to save the old names in a separate object, use closures :
ExtendedContext.prototype.fillRect = (function () {
var oldf = ExtendedContext.prototype.fillRect;
return function () {
//Do some stuff
oldf.apply (this, arguments);
//Do some more stuff
};
}) ();
If you have a bunch to do this might help :
function extend (fnc) {
var mthd = (fnc.toString ().match (/^function\s+(\w+)\s*\(/) || ['', ''])[1];
if (mthd in ExtendedContext.prototype)
throw ('ExtendContext method ' + mthd + 'does not exist');
ExtendedContext.prototype['_' + mthd] = ExtendedContext.prototype[mthd];
ExtendedContext.prototype[mthd] = fnc;
}
Then you can call extend as follows
extend (function fillrect () {
// Do some stuff
this._fillrect.apply (this, arguments);
// Do some more stuff
});
To refer to the old method use its name prefixed with '_'
I'm a few months late, but I'm using a fairly simple design to accomplish this functionality.The structure of our JavaScript runs off of a global object to keep our code secured from global vars.
For each page/usercontrol we are modifying our global object to hold a new object, but some code needs different functionality in different places, requiring extension methods. We don't want to duplicate code and redefine the whole object for the extended instance, and we don't want the code to care how it is being extended.
Instead of punching a duck until it does what you want it to, why not create a generic extension method? Using our case, here is an example:
// Using a Global JavaScript object:
GlobalNameSpace.ExtensionFunction = function(oParam1, oParam2, oParam3)
{
/// <summary>All parameters are optional</summary>
return; // For instances when it is not being overwritten, simply return
}
//In the Code to be extended:
GlobalNameSpace.Control.ControlFunction(oSender, oArgs)
{
///<summary>Control's function</summary>
// Function-y stuff..
GlobalNameSpace.ExtensionFunction(oSender, oArgs);
}
//and finally in the code to extend the functionality
GlobalNameSpace.Page.Init
{
///<summary>Initializes the page</summary>
// redefine the extension function:
GlobalNameSpace.ExtensionFunction = function(oSender, oArgs)
{
// Call the extension function, or just code the extension here
GlobalNameSpace.Page.Function(oSender, oArgs);
}
}
The short coming of this method is if you want to do this for multiple objects at a time, at which point it may be a better idea to move an extension method into the code you are specifically wanting to extend. Doing this will make that extension code less generic, but that can be decided according to your needs.
I'm sorry if this question has been asked before, but I'm not even sure what search terms to use to find the answer and when I try to search I never get anything specific to this question.
I'm using Javascript and I am wondering if it is possible to do something like this:
find(x); // find a document (for example)
find.inFolder(y); // find a folder's documents (for example)
In other words, can I have a function that can also be used as an object/class? I know I could run find() once and return a hash so that find.inFolder() would work, but I'm hoping there's a way where I could continue to call find().
Can it be done with prototype? (my "prototype" knowledge is very limited)
function find() {}
find.prototype.inFolder = function() {}
Can it be done inside a hash? [I know this code doesn't work]
var find = {
() : function() {},
inFolder : function() {}
}
To push it even further, is there a way to have the results of .inFolder() be sent to the find() function this way:
find().inFolder();
I know you might say that I don't understand the concept of javascript, and you'd be mostly correct, but I've seen people do some pretty amazing stuff with JS so I thought I'd ask the pros out there.
Thanks in advance for any help.
What you're describing is a Fluent interface (if you want something to search for). You could accomplish something like what you're trying to achieve like this:
var find = function() {
this.inFolder = function() {
return this; // Although to stop chaining, you could return nothing here.
};
return this;
};
find().inFolder(); // .inFolder().inFolder()...
This is a great pattern, especially when leveraged in projects like jQuery:
$("#element").find(".child_element").first();
Each call returns a jQuery object with .find(), .first() and many other functions, which lets you write intuitive and fluid code.
I kind of liked your find().inFolder() example, so here's an expanded version:
var find = function(file) {
this.folders = {
"Documents": ["Foo.txt", "Bar.txt"],
"Downloads": ["File.exe"],
"Misc": ["Picture.jpg"]
};
this.file = file;
this.inFolder = function(folder) {
var files = this.folders[folder];
return files.indexOf(this.file) >= 0;
};
return this;
};
alert(find("Foo.txt").inFolder("Documents")); // True
alert(find("File.exe").inFolder("Downloads")); // True
alert(find("Picture.jpg").inFolder("Downloads")); // False
http://jsfiddle.net/andrewwhitaker/TCdTd/
You can assign, a function to a member of another function:
find = function(x) { .... }
find.inFolder = function(y) { ... }
jsFiddle.
I'm not sure I understand the question however.