JavaScript

Some code paths are unreachable because the return, throw, break, and continue statements unconditionally exit a block of code. The code statements after the above keywords (which exit the code block) will not execute.

componentDidMount() is invoked immediately after a component is mounted. This method is a good place to load data from an endpoint as it is invoked before the browser updates the screen. Using setState() in componentDidMount() will trigger an extra rendering, so it causes performance issues as render() will be called twice.

The use of arguments.caller and arguments.callee make several code optimizations impossible. They have been deprecated in future versions of JavaScript and their use is forbidden in ECMAScript 5 while in strict mode.

Imports are an ES6/ES2015 standard for making the functionality of other modules available in your current module. In CommonJS this is implemented through the require() call. Why would you want to restrict imports?

The Symbol function may have an optional description:

Unused variables are generally considered a code smell and should be avoided.

A catch clause that only rethrows the original error is redundant, and has no effect on the runtime behavior of the program. These redundant clauses can be a source of confusion and code bloat, so it's better to disallow these unnecessary catch clauses.

Returning an awaited value (like with return await f()) has two problems: - It queues an extra microtask, blocking the callstack until return is executed.

Some HTML elements have native semantics that are implemented by the browser. This includes default/implicit ARIA roles. Setting an ARIA role that matches its default/implicit role is redundant since it is already set by the browser.

Enforce img alt attribute does not contain the word image, picture, or photo. Screenreaders already announce img elements as an image. There is no need to use words such as image, photo, and/or picture.

Elements with an interactive role and interaction handlers (mouse or key press) must be focusable as it will be helpful for keyboard and screen reader users.

Enforce onmouseover/onmouseout are accompanied by onfocus/onblur. Coding for the keyboard is important for users with physical disabilities who cannot use a mouse, AT compatibility, and screenreader users.

Enforces that no distracting elements are used. Elements that can be visually distracting can cause accessibility issues with visually impaired users. Such elements are most likely deprecated, and should be avoided. By default, the following elements are visually distracting: <marquee> and <blink>.

Tab key navigation should be limited to elements on the page that can be interacted with. Thus it is not necessary to add a tabindex to items in an unordered list, for example, to make them navigable through assistive technology. These applications already afford page traversal mechanisms based on the HTML of the page. Generally, we should try to reduce the size of the page's tab ring rather than increasing it.

In 2.0.0, didReceiveAttrs and didUpdateAttrs hooks were introduced. These hooks are called whenever the references of arguments to a component change. These hooks receive arguments, however one should not use them as they can be very costly when you have a lot of components on the page.

Ember does not allow deeply-nested computed property dependent keys with @each. At runtime, it will show a warning about this. You should use @each only one level deep otherwise it will create a complex equation and effect your application performance.

Interactive HTML elements indicate controls in the user interface. Interactive elements include <a href>, <button>, <input>, <select>, <textarea>. Non-interactive HTML elements and non-interactive ARIA roles indicate content and containers in the user interface. Non-interactive elements include <main>, <area>, <h1> (,<h2>, etc), <img>, <li>, <ul> and <ol>.

Non-interactive HTML elements indicate content and containers in the user interface. Non-interactive elements include <main>, <area>, <h1> (,<h2>, etc), <img>, <li>, <ul> and <ol>. Interactive HTML elements indicate controls in the user interface. Interactive elements include <a href>, <button>, <input>, <select>, <textarea>.