What are the commonly used closure functions in js?

Commonly used closure functions in js include basic closure functions, event processing, counters, modularization and delayed execution, etc. Detailed introduction: 1. The basic closure function is an internal function that can access the variables of the external function; 2. Event processing, by accessing related functions and variables, thereby realizing the event processing function; 3. Counter, each time the function is called Increase or decrease the value of the counter; 4. Modularization, organize some related functions and variables together to form an independent unit; 5. Delayed execution, delay the execution of a function until certain conditions are met, etc.

# Operating system for this tutorial: Windows 10 system, Dell G3 computer.

Closure (Closure) is a very important concept in JavaScript, which allows a function to access variables outside its lexical scope. Closure functions are widely used in JavaScript, and they can help us implement many complex functions and logic. In this article, we will explore what closure functions are commonly used in JavaScript and explain them in detail.

1. Basic closure function

The most basic closure function is an internal function that can access the variables of the external function. For example:

function outerFunction() {
  let outerVar = 'I am outer';
  function innerFunction() {
    console.log(outerVar);
  }
  return innerFunction;
}
let closureFunc = outerFunction();
closureFunc(); // 输出：I am outer

In this example, the inner function `innerFunction` can access the variable `outerVar` of the outer function `outerFunction`, which is a simple closure function.

2. Closure function and event handling

In JavaScript, we often use closure functions to handle events. For example:

function addEvent(element, type, handler) {
  element.addEventListener(type, function() {
    handler(element);
  });
}
let button = document.getElementById('myButton');
addEvent(button, 'click', function(element) {
  console.log('Button clicked:', element);
});

In this example, the `addEvent` function creates a closure function, which can access the `handler` function and the `element` variable, thus realizing the event processing function.

3. Closure function and counter

The closure function can also be used to implement the counter function. For example:

function createCounter() {
  let count = 0;
  return function() {
    count++;
    console.log(count);
  };
}
let counter = createCounter();
counter(); // 输出：1
counter(); // 输出：2
counter(); // 输出：3

In this example, the `createCounter` function returns a closure function that can access the variable `count` of the external function, thus realizing the counter function.

4. Closure function and modularization

Closure function can also be used to implement modular functions. For example:

let myModule = (function() {
  let privateVar = 'I am private';
  function privateFunction() {
    console.log(privateVar);
  }
  return {
    publicFunction: function() {
      privateFunction();
    }
  };
})();
myModule.publicFunction(); // 输出：I am private

In this example, we use the closure function to create a module that contains private variables and private functions, and exposes a public function, thereby achieving modular functionality.

5. Closure function and delayed execution

The closure function can also be used to implement the function of delayed execution. For example:

function delayExecution(func, time) {
  return function() {
    setTimeout(func, time);
  };
}
let delayedFunc = delayExecution(function() {
  console.log('Delayed execution');
}, 1000);
delayedFunc(); // 1秒后输出：Delayed execution

In this example, the `delayExecution` function returns a closure function that can delay the execution of the passed in function.

Summary

In JavaScript, closure functions are a very important concept. They can help us implement many complex functions and logic. Commonly used closure functions include basic closure functions, event handling, counters, modularization and delayed execution. By learning and applying closure functions, we can better understand the language features of JavaScript and write more flexible and efficient code. I hope this article can help you better understand the commonly used closure functions in JavaScript.

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