What does JavaScript hook function include?

JavaScript hook functions include the following types: before, after and around.

1. before hook

The before hook function is executed before the execution of the main function. Its function is to intercept the execution of the main function and perform some pre-processing on it. . The before hook is implemented by executing a function before calling the main function.

The following is a sample code:

function before(fn, beforeFn) {
  return function() {
    beforeFn.apply(this, arguments);
    return fn.apply(this, arguments);
  }
}

function mainFunc(param) {
  console.log(`执行主函数，参数为${param}`);
}

const beforeFunc = function(param) {
  console.log(`before钩子函数，参数为${param}`);
}

const newFunc = before(mainFunc, beforeFunc);

newFunc('test');

In the above sample code, we define a before function, which receives two parameters fn and beforeFn, and returns a new function. This new function first executes the beforeFn function internally, and then executes the main function fn. By executing the before function before the main function is executed, we can implement the function of the before hook.

2. after hook

The after hook function is executed after the main function is executed. Its function is to intercept the return value of the main function and perform certain operations. The after hook is implemented by executing a function after calling the main function.

The following is a sample code:

function after(fn, afterFn) {
  return function() {
    const res = fn.apply(this, arguments);
    afterFn.apply(this, arguments);
    return res;
  }
}

function mainFunc() {
  console.log(`执行主函数`);
  return 'test';
}

const afterFunc = function(res) {
  console.log(`after钩子函数，返回值为${res}`);
}

const newFunc = after(mainFunc, afterFunc);

newFunc();

In the above sample code, we define an after function, which receives two parameters fn and afterFn, and returns a new function. Internally, this new function first executes the main function fn, obtains the return value, then executes the afterFn function, and finally returns the return value. By executing the after function after the main function is executed, we can realize the function of the after hook.

3. around hook

The around hook function is a combination of before hook and after hook. It can operate before and after the main function is executed. The around hook is implemented by executing two functions before and after calling the main function.

The following is a sample code:

function around(fn, beforeFn, afterFn) {
  return function() {
    beforeFn.apply(this, arguments);
    const res = fn.apply(this, arguments);
    afterFn.apply(this, arguments);
    return res;
  }
}

function mainFunc(param) {
  console.log(`执行主函数，参数为${param}`);
  return 'test';
}

const beforeFunc = function(param) {
  console.log(`before钩子函数，参数为${param}`);
}

const afterFunc = function(res) {
  console.log(`after钩子函数，返回值为${res}`);
}

const newFunc = around(mainFunc, beforeFunc, afterFunc);

newFunc('test');

In the above sample code, we define an around function, which receives three parameters fn, beforeFn and afterFn, and returns a new function. Internally, this new function first executes the beforeFn function, then executes the main function fn, obtains the return value, and finally executes the afterFn function. By executing the before and after functions before and after the execution of the main function, we can implement the function of the around hook.

Summary

JavaScript hook function is a very common programming technique, which allows us to better control the execution flow of the program. The hook function allows us to perform some operations before and after the execution of the main function, such as input validation, logging, performance statistics, etc. In the actual development process, we can flexibly use these hook functions to achieve better programming effects.

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