这个问题在这里已有答案：

• var functionName = function() {} vs function functionName() {} 37回答

他们都有自己的用例。函数声明是hoisted到脚本的顶部，可以在定义出现之前调用，而函数表达式只能在声明后调用。

sayHello1(); // Won't work since variable expression is created after call
sayHello2(); // Will work since function declarations are hoisted

var sayHello1 = function() {
  console.log("Hello World!");
}

function sayHello2() {
  console.log("Hello World!");
}

命名函数表达式对递归调用很有用：

var sayHello1 = function sayHelloFunc() {
  if (/* something */) {
    sayHelloFunc()
  }
}

函数声明和函数表达式可以互换使用吗？ [重复]

sayHello1(); // Won't work since variable expression is created after call
sayHello2(); // Will work since function declarations are hoisted

var sayHello1 = function() {
  console.log("Hello World!");
}

function sayHello2() {
  console.log("Hello World!");
}

var sayHello1 = function sayHelloFunc() {
  if (/* something */) {
    sayHelloFunc()
  }
}