“ {”的含义是什么？ "}"大括号围绕此反应库代码？

问题描述

我正在查看React库代码。看完之后，我发现了一段特殊的代码，我无法理解它的重要性。有人可以帮忙吗？

I was going through react library code. After going through I found a special piece of code I am unable to understand its significance. Can someone help?

var validateFormat = function () {};

{
  validateFormat = function (format) {
    if (format === undefined) {
      throw new Error('invariant requires an error message argument');
    }
  };
}

为什么反应开发人员将validateFormat包装在花括号中？这样做有什么意义吗？

Here why react developer has wrapped the validateFormat into curly braces? is there any significance of doing this.

如果我执行以下操作，则其工作原理相同-

If I do the following it works the same -

var validateFormat = function () {};

validateFormat = function (format) {
   if (format === undefined) {
   throw new Error('invariant requires an error message argument');
   }
};

推荐答案

阻止范围是其。如果您查看您会发现，此函数是根据 __ DEV __ 的值有条件定义的，该值在转换过程中已优化，因为它等效于。

The block scope is a result of their babel-preset-fbjs. If you look at the original source you'll find that instead, this function is conditionally defined depending on the value of __DEV__, which is optimized out during transpilation since it is equivalent to process.env.NODE_ENV !== 'production'.

let validateFormat = () => {};

if (__DEV__) {
  validateFormat = function(format) {
    if (format === undefined) {
      throw new Error('invariant requires an error message argument');
    }
  };
}

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