What does the new keyword do in JavaScript?
It creates a new empty object, sets this to that object inside the function, runs the function body, and returns this (the new object) unless the function returns its own object.
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More FAQs in this in Constructors and the new Keyword in JavaScript
this becomes the global object (or undefined in strict mode). Properties get added to window instead of a new object. The function returns undefined. This is a common bug with function constructors.
Yes. Calling a class constructor without new throws TypeError: Class constructor X cannot be invoked without 'new'. This prevents the forgotten-new bug that function constructors have.
Yes. If you call a bound function with new, this is a new object, not the bound this. However, any preset arguments from bind still apply to the new object.
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