For now, using spread attributes allows you to control which attributes appear on an element. <div {...foo}> where foo is an object of attribute keys and values will add/remove attributes according to which are present and non-null.

for (var member in myObject) delete myObject[member]; ...would seem to be pretty effective in cleaning the object in one line of code

for (var prop in obj) { if (obj.hasOwnProperty(prop)) { delete obj[prop]; } }

Ubiquity: you can also run your validation on the server side (e.g. nodejs)

JavaScript is, of course, a dynamic language that allows you to add and remove objects and their members at any point in time. For many, this is precisely why they enjoy the language: there are very few constraints imposed by the language.

You can set options.params to a POJO as shown above, or to an instance of the JavaScript's built-in URLSearchParams class. const params = new URLSearchParams([['answer', 42]]); const res = await axios.get('https://httpbin.org/get', { params });

In contrast, an object's actual prototype (obtained with Object.getPrototypeOf) is the real and only definition of an object's nature -- even in the possible case that its prototype has been changed after creation (either though the spec compliant Object.setPrototypeOf or by changing the commonly implemented __proto__ property).

Checking if an object is a POJO can be somewhat tricky and depends on whether you consider objects created using Object.create(null) to be POJOs. The safest way is using the Object.getPrototypeOf() function and comparing the object's prototype.

mixing the turing complete of javascript with the markup of HTML eliminates the readability of JSX so that it is actually harder to parse than a solution like hyperscript

If the react cargo cult didn't have the JSX cowpath paved for them and acclimated to describing their app interface with vanilla javascript, they'd cargo cult around that. It's really about the path of least resistance and familiarity.

hyperscript is much simpler to refactor and DRY up your code than with JSX, because, being vanilla javascript, its easier to work with variable assignment, loops and conditionals.

Don't think so; template strings solve the problem JSX tries to tackle without forking the language.

This module is similar to JSX, but provided as a standards-compliant ES6 tagged template string function.

tagged template string virtual dom builder

render(html`<${Button} on:click=${() => (clicked += 1)}>Click Me!<//>`)

svelte-htm - Hyperscript Tagged Markup for svelte; a jsx-like syntax using Tagged Templates

My proposal is that we solve this by treating a static key prop as different from one provided through spread. I think that as a second step we might want to even give separate syntax such as:

by using tagged templates we can inline function calls

Use a node-style require() to organize your browser code and load modules installed by npm.

browserify is a tool for compiling node-flavored commonjs modules for the browser.

However, this would lead to further divergence. Tooling that is built around the assumptions imposed by template literals wouldn't work. It would undermine the meaning of template literals. It would be necessary to define how JSX behaves within the rest of the ECMAScript grammar within the template literal anyway.

Template literals work well for long embedded DSLs. Unfortunately the syntax noise is substantial when you exit in and out of embedded arbitrary ECMAScript expressions with identifiers in scope.

ECMAScript 6th Edition (ECMA-262) introduces template literals which are intended to be used for embedding DSL in ECMAScript.

Why not Template Literals?

This is valid javascript! Or harmony or es6 or whatever, but importantly, it's not happening outside the js environment. This also allows us to use our standard tooling: the traceur compiler knows how to turn jsx`<div>Hello</div>`; into the equivalent browser compatible es3, and hence we can use anything the traceur compile accepts!

Think of JavaScript. In the browser you don't have direct access to the file system. In Node.js you have. Same programming language. Different APIs.

x &&= 1

IMO svelte does have a responsibility to teach/demo the basics of "functional javascript" probably as a docs/tutorial/demos chapter on "the power of javascript expressions"

Hooks embrace JavaScript closures and avoid introducing React-specific APIs where JavaScript already provides a solution.

Solid supports templating in 3 forms JSX, Tagged Template Literals, and Solid's HyperScript variant.

JSX is an XML-like syntax extension to EcmaScript (https://facebook.github.io/jsx/).

use universal loading to render identical HTML on both the server and client.

Node.js code must be run by the node process, not the browser (the code must run in the server).

use Xstate which offers a finite state machine that adheres to the SCXML spec­i­fi­ca­tion and provides a lot of extra goodness, including vi­su­al­iza­tion tools, test helpers and much more

the function you pass to the find method is called a predicate. The predicate here defines a boolean outcome based on conditions defined in the function itself, so that the find method can determine which value to find.

perhaps, imo this would make more sense. but it would slow down Parcel significantly as packages who don't have a browserslist or something similar will all get compiled (and most packages actually do target commonjs, which makes this prob not such a good idea). Which unfortunately is way too many packages. It would be great if tools like babel actually enforced a similar pattern to Parcel and use browserlist file or package.json instead of allowing defining target env in babel. Or at least not encourage it.

I forgot to mention in the original issue way back that I have a lot of data. Like 1 to 3 MB that is being passed around via export let foo.

But we face our own hostile environment: underpowered devices, poor network connections, and the complexity inherent in front-end engineering.

Your problem is that you were returning the rejected loginDaoCall, not the promise where the error was already handled. loginApi.login(user, password) did indeed return a rejected promise, and even while that was handled in another branch, the promise returned by the further .then() does also get rejected and was not handled.

// LoginApi.js return loginDao.login(username, password).then(function (res) { store.dispatch(loginSuccess()); log.log("[loginApi.login] END"); return true; }, function (err) { store.dispatch(loginFail()); errorUtils.dispatchErrorWithTimeout(errorLogin); log.log(err); return false; }); // never supposed to reject

The "invisible try..catch" around the executor automatically catches the error and turns it into rejected promise.

This treatment of thenables allows promise implementations to interoperate, as long as they expose a Promises/A+-compliant then method. It also allows Promises/A+ implementations to “assimilate” nonconformant implementations with reasonable then methods.

the promise specification explicitly does not make a distinction

If you need to call the function repeatedly, this is much, much faster than using eval.

Some modules, like events or util, are built in to Node.js. If you want to include those (for example, so that your bundle runs in the browser), you may need to include rollup-plugin-node-polyfills.

Getting the JS infrastructure upgraded can take hours of Googling.

Modules using code that doesn’t exist in browsers such as process.env.NODE_ENV and forcing you to convert or polyfill it.

If you've followed React's guide, you've installed react from npm. You can teach Rollup how to find this package within your project's node_modules directory using the rollup-plugin-node-resolve plugin. Since React exports a CommonJS module, you'll also need to convert that into an ES6 module using the rollup-plugin-commonjs plugin.

This isn't really a bug, because if you have an async function that returns a function, it doesn't really return a function - it returns a promise. I don't remember whether the Svelte internals currently check for the onMount callback's return being a function or whether they check for it being truthy. Maybe there's some adjustment to be made there.

The lack of spread continues to be a big pain for me, adding lots of difficult-to-maintain cruft in my components. Having to maintain a list of all possible attributes that I might ever need to pass through a component is causing me a lot of friction in my most composable components.

By default, in order to allow inline fat-arrow validation functions, the field will not rerender if you change your validation function to an alternate function that has a different behavior. If you need your field to rerender with a new validation function, you will need to update another prop on the Field, such as key

function* enumerate(iterable) { let i = 0; for (const x of iterable) { yield [i, x]; i++; } } for (const [i, obj] of enumerate(myArray)) { console.log(i, obj); }

for (let [index, val] of array.entries())

Note that Array.entries() returns an iterator, which is what allows it to work in the for-of loop; don't confuse this with Object.entries(), which returns an array of key-value pairs.

Object.keys(obj).forEach could work, but it only includes own properties; for…in includes enumerable properties anywhere on the prototype chain.

The error callback becomes a reject, while the "happy path" callback becomes a resolve.

Here we store the three Promise objects in variables, which has the effect of setting off their associated processes all running simultaneously. Next, we await their results — because the promises all started processing at essentially the same time, the promises will all fulfill at the same time

The “shared” schema is effectively the API schema. These are the fields exchanged in the API, common to client and server.

.catch(error => download_count = error) // check for error in template

Making the value change to a Promise for the duration would be more fitting for many uses.

Migrating the stores to TypeScript

The value attribute of an input element or its children option elements must not be set with spread attributes when using bind:group or bind:checked. Svelte needs to be able to see the element's value directly in the markup in these cases so that it can link it to the bound variable.

Rest syntax looks exactly like spread syntax. In a way, rest syntax is the opposite of spread syntax. Spread syntax "expands" an array into its elements, while rest syntax collects multiple elements and "condenses" them into a single element.

One of the arguments that's frequently deployed in favour of JSX-based frameworks over template-based ones is that JSX allows you to use existing language constructs:

But what all frameworks have in common is to write JS and this could convince users of React but also newcomers that know JS.

functions present a problem again because there is no reliable way to compare two functions to see if they are semantically equivalent.

React is an isomorphic/universal framework. That means that there is a virtual representation of the UI component tree, and that is separate from the actual rendering that it outputs in the browser.

Note that to use the this context the test function must be a function expression (function test(value) {}), not an arrow function, since arrow functions have lexical context.

Now only the defined subpath in "exports" can be imported by a consumer:

Even though it works much like a function, import() is an operator

The module specifier is always fixed. That is, you can’t change what you import depending on a condition. And you can’t assemble a specifier dynamically.

Ways of delivering JavaScript source code

many organizations have been burned by the high churn in JavaScript tooling, which sadly moves projects backwards as a part of moving the web forward

This is what I love about React, it's JavaScript basically, not a DSL

find every email on a web page that you're on. The big kahuna - this works for every website. Inject it into a site with Chrome DevTools (more here)

var elems = document.body.getElementsByTagName("*");
var re = new RegExp("(^[a-zA-Z0-9_.+-]+@[a-zA-Z0-9-]+\.[a-zA-Z0-9-.]+$)");
for (var i = 0; i < elems.length; i++) {
    if (re.test(elems[i].innerHTML)) {
        console.log(elems[i].innerHTML);
    }
}

count_value

But I'll definitely take underscore mixins over extending String.prototype or other clunky implementations any day.

If you can, use AMP like any other JavaScript library to build your site and forget about the canonical linking. Using AMP to build a whole website dramatically reduces your maintenance burden.

the umbrella term "JavaScript" as understood in a web browser context contains several very different elements. One of them is the core language (ECMAScript), another is the collection of the Web APIs, including the DOM (Document Object Model)

a syntax extension to JavaScript

name provided to a function expression as above is only available to the function's own scope

supports functional programming — because they are objects, functions may be stored in variables and passed around like any other object

most common host environment is the browser, but JavaScript interpreters can also be found in a huge list of other places

When you hear there's something called "template strings" coming to JavaScript, it's natural to assume it's a built-in template library, like Mustache. It isn't. It's mainly just string interpolation and multiline strings for JS. I think this is going to be a common misconception for a while, though.

HTML templates

No built-in syntax for looping

Multi-lines strings and indented strings

localForage is a JavaScript library that improves the offline experience of your web app by using an asynchronous data store with a simple, localStorage-like API. It allows developers to store many types of data instead of just strings.

This starter takes advantage of Typescript and Emotion. This is a personal choice, and I'd encourage you to give it a shot. If you're interested in using plain ES6 and regular scss styling, see release v1 of this library.

There’s no need for nasty repetition in ES6!… // ES6 code const a = 1, b = 2, c = 3; obj = { a b c }; // obj.a = 1, obj.b = 2, obj.c = 3

// ES5-compatible code var myObject = { prop1: 'hello', prop2: 'world', output: function() { console.log(this.prop1 + ' ' + this.prop2); } }; myObject.output(); // hello world

The promises of a chain are nested like Russian dolls, but get popped like the top of a stack.

Similarly, .catch() is really just a .then() without a slot for handleFulfilled.

in the absence of an immediate need, it is simpler to leave out error handling until a final .catch() statement.

Handling a rejected promise too early has consequences further down the promise chain.   Sometimes there is no choice, because an error must be handled immediately.

Mozilla does not permit extensions distributed through https://addons.mozilla.org/ to load external scripts. Mozilla does allow extensions to be externally distributed, but https://addons.mozilla.org/ is how most people discover extensions. The are still concerns: Google and Microsoft do not grant permission for others to distribute their "widget" scripts. Google's and Microsoft's "widget" scripts are minified. This prevents Mozilla's reviewers from being able to easily evaluate the code that is being distributed. Mozilla can reject an extension for this. Even if an extension author self-distributes, Mozilla can request the source code for the extension and halt its distribution for the same reason.

Now, a couple of years later, my guidelines for JS are:

In Python, when trying to do a dubious operation, you get an error pretty soon. In JavaScript… an undefined can fly through a few layers of abstraction, causing an error in a seemingly unrelated piece of code.

function add(a,b) { return + (a + b) }
add(2,2)
add('2', 2)

I found that the overhead to use types in TypeScript is minimal (if any).

ESLint does automatic code linting

Write a new test and the result. If you want to make it REPL-like, instead of writing console.log(x.toString()) use expect(x.toString()).toBe('') and you will directly get the result.

I recommend Airbnb style JavaScript style guide and Airbnb TypeScript)

zxcvbn works identically on the server