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JavaScript is a high-level, interpreted programming language that can be used to create dynamic, interactive web pages. Its key features include event-driven programming, object-oriented programming, and support for various programming paradigms.
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Undefined is a primitive value that is automatically assigned to variables that are declared but not initialized. Null on the other hand, is an object that represents the absence of any object value.
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You can declare variables in JavaScript using the var, let or const keywords. var and let are used to declare variables that can be reassigned, while const is used to declare variables that are read-only and cannot be reassigned.
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"==" is a loose equality operator that compares two values for equality, but performs type coercion if necessary. "===" is a strict equality operator that compares two values for equality without performing type coercion.
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A closure is a function that has access to the variables in its lexical scope, even after the scope has been closed. Closures are commonly used to create private variables and functions in JavaScript.
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The "this" keyword in JavaScript refers to the object that the function is a method of. The value of "this" is determined by how the function is called.
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Synchronous programming is when the code is executed sequentially, blocking the execution until a previous operation is complete. Asynchronous programming, on the other hand, allows the code to continue executing while a previous operation is still in progress.
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Callbacks are functions that are passed as arguments to other functions and are executed when the other function has completed its task. Callbacks are commonly used in asynchronous programming to handle the results of an asynchronous operation.
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Promises are a way to handle asynchronous operations in JavaScript. Promises represent the eventual completion of an asynchronous operation and allow you to attach callbacks to be executed when the operation is complete.
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A function declaration creates a named function that can be called anywhere in the code, while a function expression creates an anonymous function that can only be called after it has been assigned to a variable.