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IIFE strange behavior linked to variables declared with let or var(与使用let或var声明的变量相关联的奇怪行为)

转载 作者：bug小助手 更新时间：2023-10-26 21:31:16 24 4
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I try to understand why the variable 'Permissions' will be typeof 'function' when Permissions declared with var but typeof 'object' when declared with let (which is the excepted behavior)

我试图理解为什么当用var声明权限时，变量‘Permises’的类型是‘Function’，而当用let声明时，变量的类型是‘Object’(这是例外行为)


With 'var' - Permissions is typeof 'function'

With‘var’-权限类型为‘Function’




var Permissions;

(function (Permissions) {
    Permissions[Permissions["ADMIN"] = 0] = "ADMIN";
    Permissions[Permissions["READ_ONLY"] = 1] = "READ_ONLY";
})(Permissions || (Permissions = {}));

console.log(typeof Permissions);




With 'let' - Permissions is typeof 'object'

WITH‘let’-权限类型为‘Object’




let Permissions;

(function (Permissions) {
    Permissions[Permissions["ADMIN"] = 0] = "ADMIN";
    Permissions[Permissions["READ_ONLY"] = 1] = "READ_ONLY";
})(Permissions || (Permissions = {}));

console.log(typeof Permissions);




I excepted both scenario to be 'object'. why using 'var' Permissions is typeof 'function'?

我认为这两种情况都是“对象”。为什么使用‘var’权限是‘Function’类型？


更多回答

try just var Permissions; console.log(typeof Permissions) it has nothing to do with IIFE - all to do with Permissions API and the subtle difference between var and let

尝试只使用var权限；console.log(类型的权限)它与生活无关-所有这些都与权限API以及var和let之间的细微差别有关

Does this answer your question? What is the difference between "let" and "var"?

这回答了你的问题吗？“let”和“var”有什么不同？

优秀答案推荐

Declaring a variable with var in a global scope makes it a property of window.
Since you haven't initialized it, it's actually pointing to the existing window.Permissions property, which is a constructor of navigator.permissions.

在全局范围内使用var声明变量使其成为Window的属性。由于您尚未对其进行初始化，因此它实际上指向现有的window.Permission属性，该属性是Navigator.Permises的构造函数。


let works differently and declares a separate variable in the current scope:

Let的工作方式不同，它在当前作用域中声明了一个单独的变量：




console.log(Permissions);
console.log(navigator.permissions.__proto__ === Permissions.prototype);

var test = 'test';
console.log(window.test);




If you put your var into a function scope, it would work like let:

如果您将var放入一个函数作用域，它的工作方式类似于let：




(function(){

  var Permissions;

  (function (Permissions) {
      Permissions[Permissions["ADMIN"] = 0] = "ADMIN";
      Permissions[Permissions["READ_ONLY"] = 1] = "READ_ONLY";
  })(Permissions || (Permissions = {}));

  console.log(typeof Permissions);

})();




Also works as let in a module scope:

也可以作为模块作用域中的let使用：




<script type="module">

var Permissions;

(function (Permissions) {
    Permissions[Permissions["ADMIN"] = 0] = "ADMIN";
    Permissions[Permissions["READ_ONLY"] = 1] = "READ_ONLY";
})(Permissions || (Permissions = {}));

console.log(typeof Permissions);

</script>




With this and other many problems inherited to var I treat var as legacy and dangerous and prohibit it with ESLint.

由于var继承了这个和其他许多问题，我将var视为遗留的和危险的，并使用ESLint禁止它。


更多回答

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