I want to have normal .command() handler that does some async calls, then decides if it will output something or throw the user into a mode. Is that possible?
If yes, how cat I set the delimiter based on my async calls? Can I set a custom .action() function for this mode dynamically?
Alternatively, is it possible to pass a context to this dynamically created mode?
You can create a second (or multiple) instance of Vorpal, with an entirely different set of commands. These could also be declared these on the fly.
By calling vorpal.show() on the new instance, this would "detach" the UI from the old Vorpal onto the new for the duration of that "mode", and it would appear to the user that you got an entirely new set of commands, delimiter, etc.
var modeA = new Vorpal().delimiter('fooland:');
var modeB = new Vorpal().delimiter('barland:');
modeA.command('foo'); // ...
modeB.command('bar'); // ...
// Only foo is present as a command.
modeA.show();
setTimeout(function(){
// Now bar is present as a command instead.
modeB.show();
}, 5000);
Related
I need to be able to change some variable's value, when app is closed.
I'm using exitEvent described here:
https://docs.nativescript.org/core-concepts/application-lifecycle
Also, i'm using local-storage plugin that works similar to javasctip's localstorage.
https://github.com/NathanaelA/nativescript-localstorage
My simple code looks like this:
var Observable = require("data/observable").Observable;
require("nativescript-dom");
var LS = require("nativescript-localstorage");
const application = require("tns-core-modules/application");
var page = require("ui/page");
exports.load = function (args) {
var page = args.object;
var model = new Observable();
var frame = require('ui/frame');
var ff = frame.getFrameById("dashboard");
var topmost = frame.topmost();
// This is exit event
application.on(application.exitEvent, (args) => {
LS.setItem('XX','111')
});
// What i will exit app, and run app again this will newer become 111,
it's null all the time
console.log(LS.getItem('XX'));
}
So, my question is - is possible to set any flag on app exit - it do not have to be localstorage (i've tested global variables to), to detect if exit was made, and based on this i can make a decisions that will help me ?
One of scenarios may be - i'm holding some flag in Localstorage that is TURE is user tapped "rememebr me" on the login screen.
So on exit i can check if he want's to be rememebered, if not i want to send user to login page and not dashboard when app is lauching....
Thank you.
EDIT:
I've tried applications-settings too, it will not work.
application.on(application.exitEvent, (args) => {
applicationSettings.setString("Name", "John Doe");
});
console.log(applicationSettings.getString("Name")); // not working
I suspect it's the issue with the nativescript-localstorage plugin. It writes the changes to file after a 250ms delay. At exit event you will give you very limited amount of time before your app is completely killed by system.
May be the Author had a reason for setting up this delay but I think its too much of time at least in this particular scenario so the changes are never written to file. You may raise a issue at the plugin's Github repo.
If you are looking for an immediate workaround, copy localstorage.js to your app and export internalSaveData from the file, so you could directly call it right after you finish setting your values.
I'm using leaflet-ajax to load geoJSON on demand. I want to find the maximum theProperty value so I can use that to scale the feature's fill colors before I add them to the map.
Here's my general approach:
function maxBinPropertyValue(theProperty) {
var theGeoJson = null;
var maxPropertyValue = 0;
var propertyValue = null;
var theGeoJson = new L.GeoJSON.AJAX(binsFileName());
theGeoJson.on('data:loaded', function() {
console.log('The data is loaded');
theGeoJson.eachLayer(function(layer) {
console.log('Looping through the layers');
propertyValue = feature.properties[theProperty];
if (propertyValue > maxPropertyValue) {
maxPropertyValue = propertyValue;
console.log('Max so far: ' + maxPropertyValue);
};
});
});
theGeoJson = null;
console.log('The final maximum value: ' + maxPropertyValue);
return maxPropertyValue;
};
I'm trying to wait for the data:loaded event, then loop through all the features to find the maximum value of theProperty, which is returned to the calling routine.
Except it doesn't work. The first console.log says 'The data is loaded'. The second and third console.logs are never reached, and the fourth and final one reports a value of 0 for maxPropertyValue.
How can I examine all the features in a featureset before styling them, in a way guaranteed to not have asynchronous problems?
PS: I'm pretty sure I can't use onEachFeature: instead of the above approach, because I need to examine every feature's property to determine the maximum value in the set before I can style any of the features.
As for your issue about inspecting your data and retrieving the maximum value, you are indeed facing the classic asynchronous concept of JavaScript.
See How do I return the response from an asynchronous call?
Asynchronism is a problem if not dealt with properly, but an advantage if correctly handled.
To put the concept shortly, you do not manage asynchronism in a "standard" sequential way, but you should rather consider parts of code (callbacks) that are executed at a later time based on events.
Whenever you provide a function as an argument, it is certainly a callback that will be executed at a later time, but very probably much later than the next instructions.
So in your case, your 2nd and 3rd console.log are within a callback, and will be executed once your data is loaded, which will happen much later than your 4th console.log.
As for your next step (styling and adding to map), you actually do not need to perform an extra AJAX call, since you already have all data available in theGeoJson variable. You simply need to refactor / restyle it properly.
It is a good approach to break your problem in small steps indeed.
Good luck!
PS: that being said, ES7 provides async and await functionalities that will emulate a sequential execution for asynchronous functions. But to be able to use those, you need latest browser versions or transpilation, which is probably more work to learn and configure as of today for a beginner than understanding how to work with async JS.
I also had this problem and had to wrap my head around this, so giving an explicit example for solution here;
// make a request with your "url"
var geojsonLayer = new L.GeoJSON.AJAX("url");
// define your functions to interact with data
function thingToDoBeforeLoadingStarts () {
// do stuff
}
function thingToDoForEachFileDownloaded () {
// do stuff
}
function thingToDoAfterAllDownloadEnds () {
// do stuff
}
// attach listeners
geojsonlayer.on("data:loading",thingToDoBeforeLoadingStarts);
geojsonLayer.on("data:progress",thingToDoForEachFileDownloaded)
geojsonLayer.on("data:loaded",thingToDoAfterAllDownloadEnds);
I admittedly know little about the inner workings of javascript, but need to make a library and would like to learn (hence asking here). I understand using the closure and exporting to window to not pollute the global namespace, but beyond that it confuses me a bit.
(function() {
var Drop = window.Drop = function() {
var files = [];
var add = function(word) {
files.push(word);
return files;
}
return {
files: files,
add: add
}
}
})()
// All of these seem to be the same?
var a = Drop();
var b = new Drop();
var c = new Drop;
// Each has their own state which is what I want.
a.add("file1");
b.add("file2");
c.add("file3");
Why are all three ways of "initializing" Drop the same?
What exactly gives them the ability to have their own state?
Is there an alternative to the return syntax to export those functions on Drop?
Is there just a flat out better best practice way of creating a self contained library like this?
I have searched around the net, but have found very little consistency on this subject.
The first way (Drop()) just calls the function as normal, so this is the global object (window in browser environments). It does its stuff and then returns an object, as you'd expect.
The second way (new Drop()) creates a new Drop object and executes the constructor with this set to that object. You do not, however, use this anywhere and return an object created from an object literal, so the Drop object is discarded and the object literal returned instead.
The third way (new Drop) is semantically the same as the second; it is only a syntactic difference.
They all have their own state because each time you call Drop, it has its own set of local variables distinct from the local variables of any other call to Drop.
You could transform your code to use the normal new syntax and prototypes. This has a few advantages: namely, you only create the add function once rather than one for each Drop call. Your modified code might look like this:
function Drop() {
this.files = [];
}
Drop.prototype.add = function(word) {
this.files.push(word);
return this.files;
};
By doing this, though, you lose being able to call it without new. There is, however, a workaround: You can add this as the first line inside function Drop:
if(!(this instanceof Drop)) {
return new Drop();
}
Since when you call it with new, this will be a Drop, and when you call it without new, this will be something other than a Drop, you can see if this is a Drop, and if it is, continue initializing; otherwise, reinvoke it with new.
There is also another semantic difference. Consider the following code:
var drop = new Drop();
var adder = drop.add;
adder(someFile);
Your code will work here. The prototype-based code will not, since this will be the global object, not drop. This, too, has a workaround: somewhere in your constructor, you can do this:
this.add = this.add.bind(this);
Of course, if your library's consumers are not going to pull the function out of the object, you won't need to do this. Furthermore, you might need to shim Function.prototype.bind for browsers that don't have it.
No. It's all a matter of taste.
Why are all three ways of "initializing" Drop the same?
// All of these seem to be the same?
var a = Drop();
var b = new Drop();
var c = new Drop;
When you use new in JavaScript to invoke a function, the value of this inside the function becomes the new object.
But the reason they're the same in your case is that you're not using this at all. You're making a separate object using object literal syntax, and returning it instead, so the new has no impact.
What exactly gives them the ability to have their own state?
Because each function invocation makes a new object, each object is entirely different for each invocation.
The functions assigned to the object are recreated in each Drop invocation, and therefore create a closure over the enclosing variable scope. As such, the files array of each invocation is continuously accessible to the functions made in each respective invocation.
Is there an alternative to the return syntax to export those functions on Drop?
Yes. Assign the functions and array to this, and remove the return statement. But that will require the use of new. Alternatively, put the functions on the .prototype object of Drop, and they'll be shared among all instances made using new, but keep the array assigned to this in the constructor so that it's not shared.
For the prototyped functions to reference the array, they would use this.files.
Is there just a flat out better best practice way of creating a self contained library like this?
JavaScript is very flexible. There are many ways to approach a single problem, each with its own advantages/disadvantages. Generally it'll boil down to taking advantage of closures, of prototypal inheritance, or some combination of both.
Here's a full prototypal inheritance version. Also, the outer (function() {})() isn't being used, so I'm going to add a variable to take advantage of it.
(function() {
var totalObjects = 0; // visible only to functions created in this scope
var Drop = window.Drop = function() {
this.files = [];
this.serialNumber = totalObjects++;
}
Drop.prototype.add = function(word) {
this.files.push(word);
return this.files;
};
})();
Since extensions can not access unsafeWindow, like Firefox can, to hook into DOM scripts am I looking for other ideas so I come to SO for help!
How about using some code to inject into DOM and sending the intercepted response to a background page, which then does some initial processing before calling a content script for final processing. When done, it answers to the background with a modified response, or the original (it depends), and the background page sends the response back to DOM which handles it to the DOM script response function.
There is just one problem with this, a background page cant communicate with the DOM.
I did a small test with injecting some code, where I output something to the console and an alert. The result wasnt good, as the alert fired but the console was empty - not even an error, which makes me wonder - what console received the output ?
function injectCode(fn){ // Executing an anonymous script
var script = document.createElement('script');
script.type = 'application/javascript';
script.textContent = '(' + fn + ')();';
document.documentElement.appendChild(script); // run the script
document.documentElement.removeChild(script); // clean up
}
var code = function(){
console.log('dom',window);
alert('code injected');
}
injectCode(code);
I also tried addEventListener, with DOMAttrModified DOMSubtreeModified DOMNodeInserted, on DOM elements that change when the DOM ajax response is fully parsed but all failed to fire.
Am I trying to do the impossible, by any means ?
Before continuing, make sure that you know the differences between the script contexts in an extension.
To inject a script from the background page, you have to execute a Content script, which on his turn injects the script as mentioned in your question / here.
Examples (using chrome.tabs.executeScript):
// null = current active tab
// Simple code, background:
chrome.tabs.executeScript(null, {
code: [
'var s = document.createElement("script");',
's.textContent = "console.log(window);";',
'(document.head||document.documentElement).appendChild(s);',
's.parentNode.removeChild(s);'
].join('\n')
});
I can imagine that this method is not doable for a big chuck of code. For a set of pre-defined scripts, you can then use two scripts: the code itself, and a helper script:
// config.js
var fn_code = function() {
console.log(window); ....
};
// helper.js
var s = document.createElement('script');
s.textContent = '(' + fn_code + ')();';
(document.head||document.documentElement).appendChild(s);
s.parentNode.removeChild(s);
// Background:
chrome.tabs.executeScript(null, {file: 'config.js'}, function() {
chrome.tabs.executeScript(null, {file: 'helper.js'});
});
Note: I did not directly link to "config.js", because that complicates the use when using manifest version 2, see "web_accessible_resources".
The previous method only shows how to execute code in one direction (background -> page). If there's a need to activate a background's function from the injected script, you have to define and listen to a custom event handler. See this answer + demo.
Because the code is injected, thus runs in the scope of the page, you have to check the console at the page.
When chrome.tabs.executeScript fails to execute the Content script (eg. because the extension does not have the permission to access a certain page), an error is logged at the console in the background page. This console can be accessed by following these steps.
I want to track a variable as I navigate around my site. How can I use jQuery to output this value without having to worry about tracking down wherever it might be affected and having it update.
var num = 1;
$(#trackvariable).text(num)
I want the above to execute constantly as it were.. I don't necessarily want to do it on a timer. Is there any way to do that?
If you want to listen to changes on a textnode, you can do something like this:
function InitListener () {
var container = document.getElementById ("textContainer");
var textNode = container.firstChild;
if (textNode.addEventListener) {
textNode.addEventListener ('DOMCharacterDataModified', OnCharacterModified, false);
}
}
This will only work in Firefox (and probably Chrome in Safari also):
https://developer.mozilla.org/en/JavaScript/Guide/Working_with_Objects#Defining_Getters_and_Setters
Off the top of my head I would say that the functions changing the variable should just call some sort of update function at the end of them? just an idea. I think even if you set up some kind of custom event it would still have to manually triggered in each function.