Typical application cases in JavaScript development-application of closures

Typical application cases of closures in JavaScript development

1. What is a closure?

Before we delve into the typical application cases of closures, we must first understand what closures are. Closure means that a function can access and operate variables outside it. Even after the external function has completed execution, the internal function can still access and use the variables of the external function. Simply put, a closure is a combination of a function and its associated reference environment.

2. The functions of closures

The functions of closures mainly include the following aspects:

1. Protect variables

Closures can limit variables scope of action to avoid global contamination. By encapsulating variables in a closure, only internal functions can access and modify these variables, and external code cannot directly access and modify the variables within the closure.

2. Implement private variables and private methods

Closures can simulate concepts similar to private variables and private methods in object-oriented programming languages. By defining variables and methods inside a closure, external code cannot directly access and call these private variables and methods.

3. Extend the life cycle of variables

Closure can extend the life cycle of variables. When a function completes execution, usually the variables defined within the function will be destroyed. But if the function returns an inner function that forms a closure and references the variables of the outer function, then these referenced variables will not be destroyed and their life cycle will be extended.

3. Typical application cases of closures

1. Counter

Closures can be used to create a simple counter and save the count through the closure's reference environment. value. Each time the counter function is called, the count value will be incremented by 1.

function counter() {
  var count = 0;
  return function() {
    count++;
    console.log(count);
  }
}

var increment = counter();
increment(); // 输出 1
increment(); // 输出 2
increment(); // 输出 3

2. Cache data

Closures can be used to cache data and save the time of repeated calculations. The calculation results are saved through the reference environment of the closure. If the same calculation request is encountered next time, the cached results will be directly returned.

function calculateSquare() {
  var cache = {};
  return function(number) {
    if (number in cache) {
      return cache[number];
    } else {
      var result = number * number;
      cache[number] = result;
      return result;
    }
  }
}

var square = calculateSquare();
console.log(square(5)); // 输出 25
console.log(square(5)); // 从缓存中获取结果，输出 25

3. Modular development

Closures can be used to implement modular development, hiding private variables and private methods inside the module, and only exposing specific public interfaces.

var module = (function() {
  var privateVariable = 10;

  function privateMethod() {
    console.log('私有方法');
  }

  return {
    publicMethod: function() {
      console.log('公共方法');
    }
  };
})();

module.publicMethod(); // 输出 "公共方法"
module.privateVariable; // 报错，无法访问私有变量
module.privateMethod(); // 报错，无法调用私有方法

The above are typical application cases of closures in JavaScript development. Through closures, functions such as protecting variables, implementing private variables and private methods, and extending the life cycle of variables can be achieved. Reasonable use of closures can improve the maintainability and readability of the code, and is an indispensable part of JavaScript development.

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