How do I manage context when exposing object methods in JS modules? - javascript

Okay, I realize this can be considered subjective, but I'm trying to better understand how to consider scope when writing modules that only expose what's needed publicly. I have a string utility that I've written as an object literal below:
const substrings = {
query: {},
text: "",
results: [],
exists: function (index) {
const exists = index >= 0
return exists
},
check: function () {
const q = this.query
const start = q.openIndex
const stop = q.closeIndex
if (q.hasOpen && !q.hasClose) {
console.log("Missing closing delimiter.")
}
if (!q.hasOpen && q.hasClose) {
console.log("Missing opening delimiter.")
}
if (q.hasOpen && q.hasClose && start > stop) {
console.log("Closing delimiter found before opening.")
}
if (!q.hasOpen && !q.hasClose && this.results.length == 0) {
console.log("No results found.")
}
const order = start < stop
const check = q.hasOpen && q.hasClose && order
return check
},
update: function () {
const q = this.query
const text = this.text
q.before = this.text.indexOf(q.open)
q.start = q.before + q.open.length
this.text = text.slice(q.start, text.length)
q.stop = this.text.indexOf(q.close)
q.after = q.stop + q.close.length
q.openIndex = q.before
q.closeIndex = q.before + q.stop
q.hasOpen = this.exists(q.openIndex)
q.hasClose = this.exists(q.stop)
const newPosition = q.start + q.after
q.position = q.position + newPosition
this.query = q
},
substrings: function () {
const q = this.query
const current = this.text.slice(0, q.stop)
const fullLength = this.text.length
this.text = this.text.slice(q.after, fullLength)
this.results.push(current)
this.update()
if (this.check()) {
this.substrings()
}
},
init: function (open, close, text) {
this.results = []
this.query = {
open,
close,
position: 0,
}
this.text = text
this.update()
},
getSubstrings: function (open, close, text) {
this.init(open, close, text)
if (this.check()) {
this.substrings()
return this.results
}
},
getSubstring: function (open, close, text) {
this.init(open, close, text)
if (this.check()) {
return this.text.slice(0, this.query.stop)
}
}
}
I want to use it as a Node module and expose the getSubstring and getSubstrings methods, but if I were to do:
module.exports = {
all: substrings.getSubstrings,
one: substrings.getSubstring
}
I would get an error due to the usage of this. I realize that if I replace this with the object var name substrings to reference it directly, it works. I could also refactor it to be one big function or smaller functions and just export the 2 I need.
I am trying to go about learning things the right way and am struggling with how I should be thinking about context. I understand how this changes here, but I feel like I'm not fully wrapping my head around how I should consider context when structuring my code.
Is there a more elegant solution to expose methods with code like this that wasn't written to separate private and public methods?

A simple solution would be to bind the exported functions to the proper calling context inside the exports object:
module.exports = {
all: substrings.getSubstrings.bind(substrings),
one: substrings.getSubstring.bind(substrings)
}
Personally, I prefer using the revealing module pattern over object literals for situations like this. With the revealing module pattern, create an IIFE that returns the desired functions, referring to local variables instead of properties on this. For example:
const { getSubstrings, getSubstring } = (() => {
let query = {}
let text = ''
let results = []
function exists(index) {
return index >= 0
}
function check() {
const q = query;
// ...
}
...
function getSubstrings(open, close, text) {
}
...
return { getSubstrings, getSubstring };
})();
module.exports = {
all: getSubstrings,
one: getSubstring
}
This is somewhat opinion-based, but code can be easier to read when there aren't any this references to worry about.

Related

Using function of an object after grabbing it from array

When I try to grab the object from the array, the type is undefined. Therefore I cannot use a method from the undefined object as it doesn't exist. I am relatively new to JavaScript and I have come straight from Java so the way of retrieving objects is kind of new to me. This is what I currently have.
var fleetAmount = 0;
var fleets = [];
function Fleet(number) {
this.number = number;
this.activities = [];
this.addActivity = function (activity) {
this.activities.push(activity);
};
fleets.push(this);
}
var getFleet = function(fleetNumber) {
return fleets[fleetAmount - fleetNumber];
}
This is where I try to grab the object and preform the function
const Fl = require(‘fleet.js’);
const fleet = Fl.getFleet(fleetNumber);
fleet.addActivity(activity);
I am also working in Node.js, which is how I am using the require method.
In combination with the answer from #audzzy I changed the getFleet() function so that it would be more efficient. I tested it out and it worked. This is what I used
function getFleet(fleetNumber) {
let result = fleets.filter(function (e) {
return e.number = fleetNumber;
})
return result[0];
}
Thanks for the help! I appreciate it.
you want to create a new fleet object and add it, not "this"..
adding "this" would cause a circular reference, where
this.fleets[i] = this (and all fleets would have the same value)
when calling get fleet, I would check that a fleet was returned from get fleet
in case amount is less than the number you send to getFleet (where according to what you posted: 1 returns the last, 2 returns second to last etc..)..
I hope this explanation makes sense.. anyways, this should work..
var fleets = [];
doStuff();
function doStuff(){
addFleet(1);
addFleet(2);
addFleet(7);
addFleet(3);
// should return null
let fleet1 = getFleetByNumber(5);
// should return the fleet with number 7, and not change the fleet with number 1
let fleet2 = getFleetByNumber(7);
if(fleet2){
fleet2.addActivity("activity");
}
console.log(`fleets: ${JSON.stringify(fleets)} \nfleet1: ${JSON.stringify(fleet1)} \nfleet2: ${JSON.stringify(fleet2)}`);
}
function addFleet(number) {
let fleet = { number: number,
activities: [] };
fleet.addActivity = function (activity) {
this.activities.push(activity);
};
fleets.push(fleet);
}
function getFleetByNumber(fleetNumber) {
return fleets.find(function (e) {
return e.number == fleetNumber;
});
}
function getFleet(fleetNumber) {
let result = null;
if(fleets.length - fleetNumber >= 0){
result = fleets[fleets.length - fleetNumber];
}
return result;
}

How to use recursion in JavaScript for try do function?

I want to make this code prettier with recursion.
findModel = function(oldModel, ...modelStyles) {
let model = oldModel.elements;
let i = 0;
try {
do {
model = model.children.find(child => child.mStyle === modelStyles[i]);
i += 1;
} while (i < modelStyles.length);
return model;
} catch (e) {
return undefined;
}
};
tried this:
findModel = function(oldModel, ...modelStyles) {
let model = oldModel.elements;
let i = 0;
if (i < modelStyles.length) {
model = model.children.find(child => child.mStyle === modelStyles[i]);
i += 1;
return model;
} else {
return undefined;
}
};
but it's still not working well. in the first code I get only the element, in the second one I get also undefined.
What did I wrong?
As amply noted in comments, you are actually never calling the function recursively.
When it comes to "pretty", I would not go for recursion, but for reduce:
var findModel = function(oldModel, ...modelStyles) {
try {
return modelStyles.reduce((model, style) => model.children.find(child => child.mStyle === style), oldModel.elements);
} catch (e) {} // No need to explicitly return undefined. It is the default
};
If you really need recursion, then first realise that your function expects a first argument type that never occurs again. Only the toplevel model has an elements property, so you can only call this function for ... the top level of your hierarchy.
To make it work, you would need another function that takes the model type as it occurs in the children:
var findModel = function(oldModel, ...modelStyles) {
function recur(model, style, ...modelStyles) {
if (style === undefined) return model;
return recur(model.children.find(child => child.mStyle === style), ...modelStyles);
}
// Need to change the type of the first argument:
try {
return recur(oldModel.elements, ...modelStyles);
} catch (e) {}
};
If you would change the code where the function is called initially, you could of course pass mainmodel.elements instead of mainmodel, so that this type difference problem is resolved. If you can make that change, then the recursive function can become:
var findModel = function(model, style, ...modelStyles) {
if (style === undefined) return model;
try {
return recur(model.children.find(child => child.mStyle === style), ...modelStyles);
} catch (e) {}
};
Still, I would prefer the reduce variant.
The point of recursive function is to call themselves into themselves. In your case, you are calling the function once, but the function never call itself so it just go through once. I'm not sure of the context so I can't fix your code but i can give you an example of recursion.
Lets say we have an object with property. Some are string, some are number and some are objects. If you want to retrieve each key of this object you would need recursion, since you don't know how deep the object goes.
let objectToParse = {
id: 10,
title: 'test',
parent: {
id: 5,
title: 'parent',
someKey: 3,
parent: {
id: 1,
title: 'grand-parent',
parent: null,
someOtherkey: 43
}
}
};
function parseParentKey(object) {
let returnedKey = [];
let ObjectKeys = Object.keys(object);
for(let i = 0; i < ObjectKeys.length; i++) {
if(typeof object[ObjectKeys[i]] === "object" && object[ObjectKeys[i]] !== null) {
// we are calling the methode inside itself because
//the current property is an object.
returnedKey = returnedKey.concat(parseParentKey(object[ObjectKeys[i]]));
}
returnedKey.push(ObjectKeys[i]);
}
return returnedKey;
}
console.log(parseParentKey(objectToParse));
I know this does not answer your question but it gives you a hint on how to use recursion properly. If your first code works, I don't see why you would need to change it in the first place.

module.export and global objects

I'm confused.
Occasionally when my web api receives data it mixes the data up between objects and it appears to me that the global object in the file is actually being persistent..
Here is the basic layout of the code
handlers.js
const something = require('./otherfile')
let handlers ={}
handlers.customers = function (data, callback) {
let acceptableMethods = ['post'];
if (acceptableMethods.indexOf(data.method) > -1) {
handlers._customers[data.method](data, callback);
} else {
callback(405);
}
};
handlers._customers = {}
handlers._customers.post = async function (data, callback) {
customer.new(data);
callback(200, 'success')
}
otherfile.js
let contacts_list = [];
let accountData = {};
module.exports = something = {
new: {
dostuff: async function (data) {
// update and reference global objects here..
accountData.name = data.name;
accountData.otherProperty = await somefunction(data.prop)
}
}
}
I expected that since it is requiring an exported module that each time it would call the exported module it would be treated as its own object, however, it seems that the object is not being treated as unique and is instead being overwritten in part and 'randomly'. This suggests to me that I may be able to export a mutating object such as an array across files
Am I correct in that the global is being persisted across multiple requests?
Would setting the global within the export object affect the behaviour of this object in any way? In this case I don't want this data to mutate.
Thanks in advance for your constructive criticisms and guidance :)
[Restructure your code so you are creating a new object on every request. Module's are cached on the first require so all of your variables and object properties will be persisted across calls.
// handler.js
const somethingFactory = require('./otherfile')
module.exports = function(){
let handlers = {}
const something = somethingFactory();
handlers.customers = function (data, callback) {
let acceptableMethods = ['post'];
if (acceptableMethods.indexOf(data.method) > -1) {
handlers._customers[data.method](data, callback);
} else {
callback(405);
}
};
handlers._customers = {}
handlers._customers.post = async function (data, callback) {
customer.new(data);
callback(200, 'success')
}
return handlers;
};
otherfile.js
module.exports = function(){
let contacts_list = [];
let accountData = {};
return {
new: {
dostuff: async function (data) {
// update and reference global objects here..
accountData.name = data.name;
accountData.otherProperty = await somefunction(data.prop)
}
}
}
};

javascript OO how to update self parameters with some JSON variable

Lets say I have a javascript object with the the following
var Settings = function () {
this.timelimit = 0;
this.locked = false;
this.expires = null;
this.age = null;
};
And then I set some get/set functions like:
Settings.prototype = {
getAllAges: function () {
return self.age;
},
getTimeLimit: function () {
return self.timelimit;
},
load: function() {
data_from_local_storage = LoadLocalStorage();
}
}
In data_from_local_storage I have JSON variables that match the above variables (timelimit, locked etc .. )
Issue is, the object var settings_ref = Settings() have all these 4 variables - but also have these 3 functions assigned in settings_ref - due to this OO behavior I need to write inside the load() function:
this.timelimit = data_from_local_storage.timelimit
this.age = data_from_local_storage.age
this.locked = data_from_local_storage.locked
Because if I'll write
this = data_from_local_storage it will destroy my object.
So how can I avoid writing all these variables one-by-one ?
w/o a for loop inside a function
in this example are just 4 but there are much much more and I cannot write it everywhere everytime
I'm looking for some .update() function like in Python or something ..
Any quick shortcut that someone know ?
You can use Object.assign() in ES2015:
load: function() {
Object.assign(this, LoadLocalStorage());
}
It's apparently not supported yet in IE, but there's a polyfill on the MDN page:
if (typeof Object.assign != 'function') {
(function () {
Object.assign = function (target) {
'use strict';
// We must check against these specific cases.
if (target === undefined || target === null) {
throw new TypeError('Cannot convert undefined or null to object');
}
var output = Object(target);
for (var index = 1; index < arguments.length; index++) {
var source = arguments[index];
if (source !== undefined && source !== null) {
for (var nextKey in source) {
if (source.hasOwnProperty(nextKey)) {
output[nextKey] = source[nextKey];
}
}
}
}
return output;
};
})();
}
(Personally I would use Object.defineProperty() to add the method, but that's verbatim from MDN.)
(edit though I guess if you don't have Object.assign() you may not have Object.defineProperty() either :)
If you store the data inside another object literal, it makes persisting things to localstorage and back a lot easier.. Here is an example..
//pretend local storage loader
function LoadLocalStorage() {
return {
timelimit: 100,
locked: true,
expires: new Date(),
age:40
}
}
var Settings = function () {
this.data = {
timelimit: 0,
locked: false,
expires: null,
age:null
}
};
Settings.prototype = {
getAllAges: function () {
return this.data.age;
},
getTimeLimit: function () {
return this.data.timelimit;
},
load: function() {
this.data = LoadLocalStorage();
}
}
var settings = new Settings;
console.log('Age before our load');
console.log(settings.getAllAges());
settings.load();
console.log('Age after our load');
console.log(settings.getAllAges());

My object isn't updating by reference, what's wrong with the logic?

I've been working with this bug for a few days now, and I think I've pinpointed the problem area, but I'm not sure why it doesn't work. I think it may have to do with a problem with passing an object by reference, but if that's the case I'm not sure how to apply that solution to my situation.
Basically, I'm working on (as a learning experience) my own implementation of dependency injection (although I've been told my structure is actually called AMD, I'll keep using "DI" until I understand more about the difference). So I'll briefly explain my code, then highlight the problematic part.
The syntax:
This is what my code should do, it's just very very simple DI.
I created scope with a string path, using "/scopeName/subScopeName:componentName" to select a scope, so that code users can select the scope while defining the component in a simple way, using a ":" to select a component from the scope.
There are no interfaces since it's so simple to type check in JS. There are no special component types such as factories, values, etc, every component is treated equally.
var JHTML = new Viziion('JHTML');
JHTML.addScope('/generate');
/* ... snip ... */
JHTML.addComponent('/generate:process', function(nodes) {
/* ... snip - the code inside isn't important here - snip ..*/
}).inject(['/generate:jsonInput']);
The inject function just takes an array of component paths in the order the component's arguments are expected.
Hooks are components stored in the hooks property, and then there's a function returnUserHandle which will return an object consisting of just the hooks, so all of the functions are hidden in closures, and you can feed the code user just the usable methods.
JHTML.addHook('generate', function(jsonInput, process) {
var html = process(jsonInput);
return html;
}).inject(['/generate:jsonInput', '/generate:process']);
var handle = JHTML.returnUserHandle();
/* HTML Generator Syntax - Client */
console.log(handle.generate());
The problem:
To point inject to the correct object intuitively, there's a focus property on the main object, and I thought I could use that.focus ( which is a reference to this.focus) within my different methods such as addComponent and inject to link new functions to the correct location in my scope model and have them still referenced in focus after being created with addComponent or after being called by the focusComponent method, and then inject could find the dependencies, and "wire" them by doing this:
that.focus = function() {
that.focus.apply(null, dependencies);
};
And I thought that would package the dependencies (an array) as a closure and when the code user calls the function, the correct dependencies get applied and that's the ball game. But nope. The functions dont seem to be passing by reference from that.focus into the scope model. that.focus updates, but the scope model does not.
What's wrong with my reference logic?
The code:
Here's a simplified version of the code. I think I've done my best to explain how it works and where exactly the reference problem I'm trying to solve is located.
/* Dependency Injection Framework - viziion.js */
function Viziion() {
var that = this;
//here's the focus property I mentioned
this.focus = null;
this.scope = {
'/': {
'subScopes': {},
'components': {}
}
};
this.hooks = {};
this.addScope = function(scopeName) {
/* the way this works inst relevant to the problem */
};
this.addComponent = function(componentName, func) {
var scopeArray = // snip
// snip - just code to read the component path
for (var i = 0; i <= scopeArray.length; i++) {
if (scopeArray[i] !== "") {
if (scope.subScopes[scopeArray[i]]) {
scope = scope.subScopes[scopeArray[i]];
} else if (i == scopeArray.length) {
// And here's where I add the component to the scope model
// and reference that component in the focus property
scope.components[scopeName] = func;
that.focus = scope.components[scopeName];
} else {
throw 'Scope path is invalid.';
}
}
}
} else {
throw 'Path does not include a component.';
}
return that;
};
this.returnComponent = function(componentName, callback) {
/* ... snip ... */
};
this.addHook = function(hookName, func) {
/* ... snip ... */
};
this.inject = function(dependencyArray) {
if (dependencyArray) {
var dependencies = [];
for (var i = 0; i < dependencyArray.length; i++) {
that.returnComponent(dependencyArray[i], function(dependency) {
dependencies.push(dependency);
});
}
that.focus = function() {
that.focus.apply(null, dependencies);
};
return that;
}
};
/* ... snip - focusComponent - snip ... */
/* ... snip - returnUserHandle - snip ... */
This should, when applied as shown up above under the "Syntax" header, produce a console log with a string of HTML.
Instead, I get TypeError: undefined is not a function, corresponding to the line var html = process(jsonInput);.
If you want to test the full code, all together, here it is:
/* Dependency Injection Framework - viziion.js */
function Viziion(appName) {
if (typeof appName == 'string') {
var that = this;
this.name = appName;
this.focus = null;
this.scope = {
'/': {
'subScopes': {},
'components': {}
}
};
this.hooks = {};
this.addScope = function(scopeName) {
if (typeof scopeName == 'string') {
var scopeArray = scopeName.split('/');
var scope = that.scope['/'];
for (var i = 0; i < scopeArray.length; i++) {
if (scopeArray[i] !== "") {
if (scope.subScopes[scopeArray[i]]) {
scope = scope.subScopes[scopeArray[i]];
} else {
scope.subScopes[scopeArray[i]] = {
'subScopes': {},
'components': {}
};
}
}
}
} else {
throw 'Scope path must be a string.';
}
return that;
};
this.addComponent = function(componentName, func) {
if (typeof componentName == 'string') {
var scopeArray = componentName.split(':');
if (scopeArray.length == 2) {
var scope = that.scope['/'];
var scopeName = scopeArray[1];
scopeArray = scopeArray[0].split('/');
for (var i = 0; i <= scopeArray.length; i++) {
if (scopeArray[i] !== "") {
if (scope.subScopes[scopeArray[i]]) {
scope = scope.subScopes[scopeArray[i]];
} else if (i == scopeArray.length) {
scope.components[scopeName] = func;
that.focus = scope.components[scopeName];
} else {
throw 'Scope path is invalid.';
}
}
}
} else {
throw 'Path does not include a component.';
}
} else {
throw 'Component path must be a string.';
}
return that;
};
this.returnComponent = function(componentName, callback) {
if (typeof componentName == 'string') {
var scopeArray = componentName.split(':');
if (scopeArray.length == 2) {
var scope = that.scope['/'];
var scopeName = scopeArray[1];
scopeArray = scopeArray[0].split('/');
for (var i = 0; i <= scopeArray.length; i++) {
if (scopeArray[i] !== "") {
if (i == scopeArray.length) {
callback(scope.components[scopeName]);
} else if (scope.subScopes[scopeArray[i]]) {
scope = scope.subScopes[scopeArray[i]];
} else {
throw 'Scope path is invalid.';
}
}
}
} else {
throw 'Path does not include a component.';
}
} else {
throw 'Component path must be a string.';
}
};
this.addHook = function(hookName, func) {
if (typeof hookName == 'string') {
that.hooks[hookName] = func;
that.focus = that.hooks[hookName];
} else {
throw 'Hook name must be a string.';
}
return that;
};
this.inject = function(dependencyArray) {
if (dependencyArray) {
var dependencies = [];
for (var i = 0; i < dependencyArray.length; i++) {
that.returnComponent(dependencyArray[i], function(dependency) {
dependencies.push(dependency);
});
}
console.log(that.focus);
that.focus = function() {
that.focus.apply(null, dependencies);
};
console.log(that.focus);
console.log(that.scope);
return that;
}
};
this.focusComponent = function(componentPath) {
that.focus = that.returnUserHandle(componentPath);
};
this.returnUserHandle = function() {
return that.hooks;
};
} else {
throw 'Viziion name must be a string.';
}
}
/* JSON HTML Generator - A Simple Library Using Viziion */
var JHTML = new Viziion('JHTML');
JHTML.addScope('/generate');
JHTML.addComponent('/generate:jsonInput', [{
tag: '!DOCTYPEHTML'
}, {
tag: 'html',
children: [{
tag: 'head',
children: []
}, {
tag: 'body',
children: []
}]
}]);
JHTML.addComponent('/generate:process', function(nodes) {
var html = [];
var loop = function() {
for (var i = 0; i < nodes.length; i++) {
if (nodes[i].tag) {
html.push('<' + tag + '>');
if (nodes[i].children) {
loop();
}
html.push('</' + tag + '>');
return html;
} else {
throw '[JHTML] Bad syntax: Tag type is not defined on node.';
}
}
};
}).inject(['/generate:jsonInput']);
JHTML.addHook('generate', function(jsonInput, process) {
console.log('Process func arg:');
console.log(process);
var html = process(jsonInput);
return html;
}).inject(['/generate:jsonInput', '/generate:process']);
var handle = JHTML.returnUserHandle();
/* HTML Generator Syntax - Client */
console.log(handle.generate());
Big question, bigger answer. Let's get started.
Heavy OOP, Proper Scope
First and foremost, from your code, it looks like you maybe don't fully grasp the concept of this.
Unless you change the execution context of an object's methods beforehand, said object's methods always have their contextual this bound to the object instance.
That is:
function A () {
var that = this;
this.prop = 1;
this.method = function () {
console.log(that.prop);
};
}
new A().method();
is generally equivalent to:
function A () {
this.prop = 1;
this.method = function () {
console.log(this.prop);
};
}
new A().method();
unless method is adjusted before execution with .bind, .call, or .apply.
Why does this matter? Well, if we use our this context properly we can utilize object prototypes. Prototypes serve as a far more elegant solution to defining every method of an object on a per-instance basis.
Here we create two instances, but only ever one method.
function A () {
this.prop = 1;
}
A.prototype.method = function () {
console.log(this.prop);
};
new A().method();
new A().method();
This is important for clarity, and later on is important when you are binding contexts and arguments to functions (!).
Code Hygiene
You can skip this topic if you like (head down to The Problems(s)), since it might be considered out of place, but keep in mind it does relate to part of the problem with the code.
Your code is hard to read.
Here are some thoughts on that.
Prototypes
Use them. You shouldn't need to worry about users changing execution contexts on you, as that's probably a misuse of your program. Security shouldn't be a concern considering they have the source code.
Not much else to say here.
Exit early
If you're doing sanity checks, try to opt out as early in your code as you can. If you need to throw because of a type mismatch, throw right then and there - not 27 lines later.
// Not great
if (typeof input === 'string') {
...
} else throw 'it away';
// Better
if (typeof input !== 'string') throw 'it away';
...
This goes for loops as well - making appropriate use of the continue keyword. Both of these things improve code clarity, and reduce nesting and code bloat.
Loop caching
When you're looping over a data structure, and you plan to use the current element several times within the block, you should save that element in a variable. Accessing elements and properties isn't necessarily a free-OP.
// Not great
for (var i = 0; i < myArray.length; i++) {
if (myArray[i] > 5) callback(myArray[i]);
internalArray.push(myArray[i]);
}
// Better
var len = myArray.length, element;
for (var i = 0; i < len; i++) {
element = myArray[i];
if (element > 5) callback(element);
internalArray.push(element);
}
When used correctly this improves both clarity and performance.
The Problem(s)
First off, what are we really doing here? The whole problem boils down to an overly complicated application of function binds. That is, simply changing the execution contexts of functions.
I'll also state outright that this program has no bug - it's just flawed.
The major crux of the problem would be these three lines
that.focus = function() {
that.focus.apply(null, dependencies);
};
found in the inject method. They don't make any sense. This would cause an infinite recursion, plain and simple. When you define that function, it doesn't care at all what the focus property of that is right then and there. That matters solely at execution time.
Lucky for us, we never actually get that far, since the process component doesn't get bound correctly.
A huge part of the problem is the focus property. In your program, you're using this as a sort of most recent action. A singular history as to what has just occurred. The problem is, you've tried to hot-swap this value in strange ways.
The focus property (and as you'll see later, other properties) is needed however, because of the reverse application of inject. The way you've structured your component/hook registers into inject model requires state to be held between method invocations.
As an end note for this section, the process component function definition would never have returned anything. Even if your model was correct, your input was flawed. handle.generate() would have returned undefined always.
The Answer(s)
So how can we fix this? Well, the first idea would be to scrap it, honestly. The reverse injection model is ugly, in my opinion. The level of indirection involved with the inject method is very confusing from the surface.
But then we wouldn't learn anything, would we?
So really, how do we fix this? Well, much to the dismay of the functional programmers reading, we need to hold more state.
On its own, our focus property can't provide enough information to properly change the execution contexts of our functions.
On top of our focus, which will simply hold a reference to our most recent component value, we need the field (component/hook name), and the fragment (component object, nothing if hook).
Using these two or three values inside inject, we can take our depedancies array, bind it to our focus, and set the resulting function back into our field.
The great thing about the next part is we can actually drop our closure by making the contextual this of our component/hook the unbound function.
The whole operation looks like this:
var focus = this.focus,
fragment = this.fragment,
field = this.field,
hook = function hook () {
return this.apply(null, arguments);
}, func;
dependencies.unshift(focus);
func = Function.prototype.bind.apply(hook, dependencies);
if (fragment) fragment[field] = func;
else this.hooks[field] = func;
Most of this should be pretty straight forward, but there is one piece that may give people some issues. The important thing to remember is we are essentially creating two functions in sequence here, 'discarding' the first in a sense. (It should be noted that this can be done another way with hook.bind.apply, but it creates even more confusing code. This is about as elegant as you can get.)
dependencies.unshift(focus);
func = Function.prototype.bind.apply(hook, dependencies);
First, we add our focus (our original function) to the front of our list of dependencies. This is important in a moment.
Then we invoke Function.prototype.bind using Function.prototype.apply (remembering that function prototype methods also share the function prototype methods. Pretty much turtles all the way down).
Now we pass our bind context, hook, and our prefixed dependencies to apply.
hook is used as the host for bind, whose contextual this is altered by the first element of the array of arguments passed to apply. The remaining elements are unrolled to shape the subsequent arguments of bind, thus creating the bound arguments of the resulting function.
This isn't a very simple concept, so take your time.
The other thing to note is I've dropped focusComponent completely. Its implementation didn't make sense in context. Your model relies on a last input injection, so you'll need to re-implement focusComponent as a method that simply adjusts the focus, field, and fragment states.
A small sub-fix is the process component function. Not going to go into detail here. You can compare and contrast with your original code, the differences are pretty obvious.
JHTML.addComponent('/generate:process', function (nodes) {
return (function build (struct, nodes) {
var length = nodes.length, node, tag;
for (var i = 0; i < length; i++) {
node = nodes[i];
tag = node.tag;
if (!tag) throw '[JHTML] Bad syntax: Tag type is not defined on node.';
struct.push('<' + tag + '>');
if (node.children) {
build(struct, node.children)
struct.push('</' + tag + '>');
}
}
return struct;
}([], nodes));
}).inject(['/generate:jsonInput']);
The Code
Below is what I would consider a fixed version of your code. It's written in a style that I find useful for both clarity and performance.
/* Dependency Injection Framework - viziion.js */
function Scope () {
this.subScopes = {};
this.components = {};
}
function Viziion (appName) {
if (typeof appName !== 'string') throw 'Viziion name must be a string.';
this.name = appName;
this.working = this.field = this.focus = null
this.scope = { '/': new Scope() };
this.hooks = {};
}
Viziion.prototype.addScope = function (scopeName) {
if (typeof scopeName !== 'string') throw 'Scope path must be a string.';
var scopeArray = scopeName.split('/'),
scope = this.scope['/'],
len = scopeArray.length,
element, sub;
for (var i = 0; i < len; i++) {
element = scopeArray[i];
if (element === '') continue;
sub = scope.subScopes[element]
if (sub) scope = sub;
else scope.subScopes[element] = new Scope();
}
return this;
};
Viziion.prototype.addComponent = function (componentName, func) {
if (typeof componentName !== 'string') throw 'Component path must be a string.';
var scopeArray = componentName.split(':'),
len, element, sub;
if (scopeArray.length != 2) throw 'Path does not include a component.';
var scope = this.scope['/'],
scopeName = scopeArray[1];
scopeArray = scopeArray[0].split('/');
len = scopeArray.length;
for (var i = 0; i <= len; i++) {
element = scopeArray[i];
if (element === '') continue;
sub = scope.subScopes[element];
if (sub) scope = sub;
else if (i === len) {
this.fragment = scope.components;
this.field = scopeName;
this.focus = scope.components[scopeName] = func;
}
else throw 'Scope path is invalid';
};
return this;
};
Viziion.prototype.returnComponent = function (componentName, callback) {
if (typeof componentName !== 'string') throw 'Component path must be a string.';
var scopeArray = componentName.split(':'),
len, element, sub;
if (scopeArray.length != 2) throw 'Path does not include a component.';
var scope = this.scope['/'],
scopeName = scopeArray[1];
scopeArray = scopeArray[0].split('/');
len = scopeArray.length;
for (var i = 0; i <= len; i++) {
element = scopeArray[i];
if (element === '') continue;
sub = scope.subScopes[element]
if (i === len) callback(scope.components[scopeName]);
else if (sub) scope = sub;
else throw 'Scope path is invalid';
}
};
Viziion.prototype.addHook = function (hook, func) {
if (typeof hook !== 'string') throw 'Hook name must be a string.';
this.fragment = null;
this.field = hook;
this.focus = this.hooks[hook] = func;
return this;
};
Viziion.prototype.inject = function (dependancyArray) {
if (!dependancyArray) return;
var dependencies = [],
len = dependancyArray.length,
element;
function push (dep) { dependencies.push(dep); }
for (var i = 0; i < len; i++) {
element = dependancyArray[i];
this.returnComponent(element, push);
}
var focus = this.focus,
fragment = this.fragment,
field = this.field,
hook = function hook () {
return this.apply(null, arguments);
}, func;
dependencies.unshift(focus);
func = Function.prototype.bind.apply(hook, dependencies);
if (fragment) fragment[field] = func;
else this.hooks[field] = func;
return this;
};
Viziion.prototype.returnUserHandle = function () { return this.hooks; };
/* JSON HTML Generator - A Simple Library Using Viziion */
var JHTML = new Viziion('JHTML');
JHTML.addScope('/generate');
JHTML.addComponent('/generate:jsonInput', [{
tag: '!DOCTYPE html'
}, {
tag: 'html',
children: [{
tag: 'head',
children: []
}, {
tag: 'body',
children: []
}]
}]);
JHTML.addComponent('/generate:process', function (nodes) {
return (function build (struct, nodes) {
var length = nodes.length, node, tag;
for (var i = 0; i < length; i++) {
node = nodes[i];
tag = node.tag;
if (!tag) throw '[JHTML] Bad syntax: Tag type is not defined on node.';
struct.push('<' + tag + '>');
if (node.children) {
build(struct, node.children)
struct.push('</' + tag + '>');
}
}
return struct;
}([], nodes));
}).inject(['/generate:jsonInput']);
JHTML.addHook('generate', function (jsonInput, process) {
return process(jsonInput);
}).inject(['/generate:jsonInput', '/generate:process']);
var handle = JHTML.returnUserHandle();
console.log(JHTML);
/* HTML Generator Syntax - Client */
console.log(handle.generate());

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