javascript - 如何使用箭头函数编写这个回调代码？

Question

这里是 JavaScript 和箭头函数的初学者。

我尝试将以下语法更改为箭头函数格式但失败。

正常功能:

function add(a, b, callback) {
    document.write(`The sum of ${a} and ${b} is ${a + b}.` + `<br>`);
    callback();
}

function secondLine(){
document.write("The callback must be printed after addition.");
}

add(1,2,secondLine)

箭头函数

((a, b, callback) => {
document.write(`The sum of ${a} and ${b} is ${a + b}.` + `<br>`);
callback();
})

(secondLine() => {
document.write("The callback must be printed after addition.");
})

(1,2,secondLine)

控制台只返回

The sum of function(){document.write("The callback must be printed after addition.");} and undefined is function(){document.write("The callback must be printed after addition.");}undefined.

我不应该在回调中使用箭头函数吗？如果我真的想使用回调，语法应该如何输入？

提前非常感谢。

Answer 1

您可以尝试以下方法:

(function(){
  var add = (a, b, callback) => {
    document.write(`The sum of ${a} and ${b} is ${a + b}.` + `<br>`);
    callback();
  }

  var secondLine = () => {
    document.write("The callback must be printed after addition.");
  }
  add(1,2,secondLine);
})();