You should use const and let in most cases in your modern JavaScript code.
ReadYou can use Template Literals (Strings) in ES6 to concatenate strings. Also, you can use string interpolation and multi-line strings here.
ReadThis is not a good idea to use a regular expression to validate an email address in JavaScript. If you are okay with some disadvantages, there is an option.
Readfor...in and for...of in JavaScript help us iterate over properties(keys) and values of an object.
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