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JavaScript passes every argument by value. For an object, the copied value is a reference to that object, so the caller and function can still reach the same underlying object. This explains why changing a property affects the caller, but assigning a new object to the parameter does not.

A closure is a function together with access to the variables in the scope where it was created. That access remains available even after the outer function has finished running. Closures are useful for private state, callbacks and functions configured with some remembered value.

A prototype is an object from which another object can inherit properties and methods. When a property is missing on an object, JavaScript follows its prototype chain until it finds the property or reaches null. Classes provide structured syntax for constructing objects and sharing methods through that mechanism.

Spread syntax creates a new outer object or array by copying its enumerable contents. It is a shallow copy, so nested objects are still shared references. This matters when updating React state or copying request data that another part of the application may modify.

Debouncing and throttling control how frequently a function runs when events arrive repeatedly. Debouncing waits for a quiet period, while throttling limits execution frequency during continued activity. They reduce unnecessary work but introduce different delays and must match the user experience.

this is the receiver used when a regular function runs, and its value usually depends on how the function is called. Arrow functions do not create their own this; they use the surrounding one. This matters when a method is passed as a callback and loses its original receiver.

var, let and const declare variables, but they have different scope and initialization rules. let and const are block-scoped, making it easier to keep a variable inside the code that needs it. const prevents reassignment of the binding; it does not make an object immutable.

JavaScript passes every argument by value. For an object, the copied value is a reference to that object, so the caller and function can still reach the same underlying object. This explains why changing a property affects the caller, but assigning a new object to the parameter does not.

A closure is a function together with access to the variables in the scope where it was created. That access remains available even after the outer function has finished running. Closures are useful for private state, callbacks and functions configured with some remembered value.

A prototype is an object from which another object can inherit properties and methods. When a property is missing on an object, JavaScript follows its prototype chain until it finds the property or reaches null. Classes provide structured syntax for constructing objects and sharing methods through that mechanism.

Spread syntax creates a new outer object or array by copying its enumerable contents. It is a shallow copy, so nested objects are still shared references. This matters when updating React state or copying request data that another part of the application may modify.

Debouncing and throttling control how frequently a function runs when events arrive repeatedly. Debouncing waits for a quiet period, while throttling limits execution frequency during continued activity. They reduce unnecessary work but introduce different delays and must match the user experience.

this is the receiver used when a regular function runs, and its value usually depends on how the function is called. Arrow functions do not create their own this; they use the surrounding one. This matters when a method is passed as a callback and loses its original receiver.

var, let and const declare variables, but they have different scope and initialization rules. let and const are block-scoped, making it easier to keep a variable inside the code that needs it. const prevents reassignment of the binding; it does not make an object immutable.

JavaScript learning module

JavaScript learning module