The binary data of a local file selected by the user can be retrieved using the readAsBinaryString method of a FileReader object.

Without cookies being enabled in the browser, some web applications may not work as expected. To prevent such cases navigator.cookieEnabled property can be used to do a prior check whether cookies are enabled or not.

Browsers allow user-sensitive and low-level web APIs to execute only when the page is in a secure context. In addition, the window.isSecureContext property can be used to check whether the current environment is safe or not.

The Array.fill() method can be used to fill an array with a specific value, starting from a given index and ending upto another index.

Flattening an array refers to the process taking an input array, which may itself contain n-dimensional arrays as its elements, to a single array. This can be done in Javascript using the flat() method.

The Intl.NumberFormat object can be used to format a number as a currency using Javascript. Various options can be set to customize format of currency code, comma / decimal separators etc.

The finally() callback can be used to know whether the Promise was settled. We don't care whether it was resolved or rejected.

The nullish coalescing operator has been newly introduced in Javascript. This can be used to give default values if a variable is either null or undefined.

Time delay for setTimeout() / setInterval() methods executing on inactive browser tabs are set to one second regardless of their value defined in code.

When a fixed-position modal dialog is opened, scrollbars on the page can be removed by dynamically setting overflow:hidden CSS for the 〈body〉tag.

The Object.seal() method seals an object. After an object gets sealed, no new properties can be added to it.

The Object.freeze() method can make an object or array immutable. No changes can be made to that object once it gets immutable.

Hashbang comments is the third type of syntax for adding comments to Javascript code. This comment can specify the Javascript interpreter that is to be used to execute the code within a script file or a module.

A stylesheet can include the disabled attribute in its markup to prevent it from being downloaded on page load. Later when the stylesheet needs to loaded on demand, its disabled attribute can be removed with Javascript.

Numeric separators can be used to improve readability of large numbers. For example the number 111111111111111111111111, which is difficult to read, can be alternately written as 111_111_111_111_111_111_111_111

Sometimes we would like to detect when the subtitles change in the playing video. This can be done by listening to the cuechange event on the 〈track〉element.

It is very common to access current this context inside jQuery AJAX's response callbacks (success or error). This tutorial describes 3 ways of doing this.

The Page Visibility API can be used to check whether a browser tab is active or not, i.e. if the page is in view or hidden from view.

Google Fonts can be loaded through Javascript using the Web Font Loader Library. Events are also triggered when fonts are being loaded, or when they are rendered.

A UNIX timestamp can be converted to the required date and time formats in Javascript using the Date() object and its methods.