函数组件中定义函数组件弊端

嵌套函数定义在执行的时候，每次生成的是个新函数对象。这个告诉我们，不要在函数组件里定义子函数组件，函数执行的时候子函数组件会被先卸载再挂载的。

示例

const funs1=[],funs2=[];
function funParent() {
    funChil1();
    funChil2();
    function funChil1() {
      funs1.push(funChil1);
    }
}
function funChil2() {
  funs2.push(funChil2);
}
funParent();
funParent();
console.log("fun1:",funs1[0]===funs1[1]);
console.log("fun2:",funs2[0]===funs2[1]);

ECMAScript 标准文档查找过程

• [Function Object [[Call]]](https://262.ecma-international.org/12.0/#sec-ecmascript-function-objects-call-thisargument-argumentslist)
  • PrepareForOrdinaryCall
    • NewFunctionEnvironment
      • Function Environment Records
  • OrdinaryCallEvaluateBody
    • Runtime Semantics: EvaluateBody
    • Runtime Semantics: EvaluateFunctionBody
      • FunctionDeclarationInstantiation
        • b. Let fo be InstantiateFunctionObject of f with argument lexEnv.
          • 2. Let F be OrdinaryFunctionCreate(%Function.prototype%, sourceText, FormalParameters, FunctionBody, non-lexical-this, scope)
            • Let F be ! OrdinaryObjectCreate(functionPrototype, internalSlotsList).