在 TypeScript 中导入 JSON 文件

The import form 和 the module declaration need to agree about the shape of the module, about what it exports.

When you write (a suboptimal practice for importing JSON since TypeScript 2.9 when targeting compatible module formats^{see note})

declare module "*.json" {
  const value: any;
  export default value;
}

您的意思是，所有具有以.json结尾的说明符的模块都有一个导出named default.

There are several ways you can correctly consume such a module including

import a from "a.json";
a.primaryMain

和

import * as a from "a.json";
a.default.primaryMain

和

import {default as a} from "a.json";
a.primaryMain

和

import a = require("a.json");
a.default.primaryMain

The first form is the best 和 the syntactic sugar it leverages is the very reason JavaScript has default exports.

However I mentioned the other forms to give you a hint about what's going wrong. Pay special attention to the last one. require gives you an object representing the module itself 和 not its exported bindings.

So why the error? Because you wrote

import a = require("a.json");
a.primaryMain

然而，你们的"*.json"并没有申报名为primaryMain的出口.

All of this assumes that your module loader is providing the JSON as the default export as suggested by your original declaration.

Note: Since TypeScript 2.9, you can use the --resolveJsonModule compiler flag to have TypeScript analyze imported .json files 和 provide correct information regarding their shape obviating the need for a wildcard module declaration 和 validating the presence of the file. This is not supported for certain target module formats.