How do closures help with data privacy in JavaScript?
By declaring variables inside a function and returning methods that access them. The variables are in the function's lexical environment and cannot be accessed directly from outside, only through the returned methods. This is the module pattern.
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More FAQs in Closures: Real-World Use Cases in JavaScript
Data privacy, memoization, once-utilities, currying, event handlers with state, throttle/debounce, function factories, and iterator-like patterns. Anywhere a function needs to remember variables from where it was defined, closures are used.
The memoize function closes over a cache object. The returned function checks the cache before calling the original function. If the result is cached, it returns immediately. Otherwise, it computes, stores, and returns. The cache is private to the closure.
They close over a timer variable. Each call clears the previous timer and sets a new one. The closed-over timer persists across calls, which is what makes debounce and throttle work.
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