I'm trying to load a dynamically generated JSON file into my javascript app - but I keep running into issues.
NOTE: I'm not using Node.js, just straight up vanilla javascript.
Everything I read said to do this with Webpack and their website clearly states that: beginning with Webpack version 2.0.0 json loaders are no longer needed.
Well right now I'm trying the following in my app.js file and getting an error:
import * as contractArtifact from "../build/contracts/MySmartContract.json"
The error is:
import declarations may only appear at top level of a module
NOTE: that MySmartContract.json file that I'm trying to load is not static; it's dynamically generated and has to be loaded anew every time.
I'm very new to webpack but I'm pretty sure I've installed every single package that I might need for this - according to the million tutorials I've gone through.
Here's what's in my package.json file right now:
...
"scripts": {
"serve": "webpack && node server.js"
},
"devDependencies": {
"#babel/template": "^7.10.4",
"file-loader": "^6.2.0",
"json5-loader": "^4.0.1",
"lite-server": "^2.6.1",
"webpack": "^5.6.0",
"webpack-cli": "^4.2.0"
}
...
And my webpack.config.js file looks like this:
const path = require("path");
module.exports = {
entry: "./src/js/index.js",
output: {
filename: "myCode.js",
path: path.resolve(__dirname, "FinalCode")
},
resolve: {
extensions: ['.wasm', '.mjs', '.js', '.json']
}
};
So what exactly needs to be added or tweaked in all this - and how am I finally importing that .json file into my javascript app? Am I using an import statement? A require statement? Or something else?
Are you doing this import inside a function/if or something else? The error seems to suggest that.
Imports need to be static (unless you use dynamic imports that are a promise function) a difference with require that can be used anywhere.
Try putting that line on the top of the file and also rewrite it like this
import contractArtifact from "../build/contracts/MySmartContract.json"
You can change your MySmartContract.json to MySmartContract.js and the code inside will be:
export const MySmartContract = [{Your json data}]
end them import:
import { MySmartContract } from "../build/contracts/MySmartContract.js"
or try
import MySmartContract from "../build/contracts/MySmartContract.js"
then MySmartContract will be a JSONObject or JSONArray it depend on your json data
after some google searched,
I am doing this in plugins/callApi.js
import axios from 'axios';
import Vue from 'vue';
Vue.use(callApi);
export default async (apiUrl, postData, headers = {}) => {
let msg = await axios.post(https://my-api-location.com' + apiUrl,postData);
return msg.data;
};
then set in nuxt.config.js
plugins: [
'~plugins/callApi.js']
when I want to use it
const msgData = await callApi('/api/news/getNewsList', postData);
if (msgData.response === 'success') { .......
but when I start yarn dev, it hightlight "Vue.use(callApi);" part and says "callApi is not defined"
how cant I fix it? thanks a lot :)
I actually re-read your answer because I was a little confused.
So, in your callApi.js, you define what you want there, but you are calling Vue.use(callApi) in the file where you are actually defining what callApi will be.
At the moment the compiler goes to Vue.use(callApi), this variable "callApi" is not defined yet (because it will only be available after it finishes compiling this very file).
So just do the
import axios from 'axios';
import Vue from 'vue';
export default async (apiUrl, postData, headers = {}) => {
let msg = await axios.post(https://my-api-location.com' + apiUrl,postData);
return msg.data;
};
then, by setting the plugin path on the plugins property in the nuxt.config file (exactly the way you did), the very callApi file will be automatically called (try to put a console log in your callApi file, and you'll see it logging when you start your application).
An example of what you want:
https://codesandbox.io/s/nuxt-app-demovue-ssr-forked-s94rz?file=/pages/index.vue
Now in your plugin, you have to decide exactly what you want to do. you might want to expose the function or make it globally available, that's up to you!
For this last option, you might want to take a look here:
Vue/Nuxt: How to define a global method accessible to all components?
Good luck!
I have one json file at root:
config.json
{ "base_url": "http://localhost:3000" }
and in my service class, I want to use it in this way:
private productsUrl = config.base_url + 'products';
I've found a ton of posts with either solutions that require a http.get request to load that one file to get that one variable or outdated solutions for angular.js (angular 1)
I cant believe there isnt an easier way to include this file that we already have in place without having to make an additional request to the server.
In my opinion, I would have expected that at least the bootstrapping function would be able to provide this kind of functionality, something like:
platformBrowserDynamic().bootstrapModule(AppModule, { config: config.json });
btw, this works, but its not the ideal solution:
export class Config {
static base_url: string = "http://localhost:3004/";
}
and the use it where you need it:
private productsUrl = Config.base_url + 'products';
Its not ideal, because I will have to create the class (or replace properties) in a build script. (exactly what I was thinking to do with the config.json file).
I still prefer the config.json file approach, since it would not be intrusive with the TypeScript compiler. Any ideas how to do are welcome and really appreciated!
This link explains how to use System.js to load json files in an angular app.
Special thanks to #eotoole that pointed me in the right direction.
If the link above is not clear enough, just add a map into the System.js conf. like this:
map: { 'plugin-json': 'https://unpkg.com/systemjs-plugin-json' }*
*(using external package)
or
map: { 'plugin-json': 'plugin-json/json.js' }**
**if you download the plugin from:
official system.js plugin
now I can use:
const config = require('./config.json');
anywere in my app.
and since it is official from the "systemjs" - guys, I feel comfortable using it to load app settings like base_url or other endpoints.
Now I need to figure out how to encapsulate this logic for testing purposes. Maybe requiring the file in its own class and replacing the values for the specific test case.
Are you using webpack? If you are, and you can just do
const config = require('./config.json');
#Injectable()
export class MyService {
private config:any = config;
....
}
in your webpack config you will need the json-loader
...
module: {
...
loaders: [
...
{
test: /\.json$/,
loaders: ["json-loader"]
},
...
]
}
...
How can I access a JSON file in ECMAScript 6?
The following doesn't work:
import config from '../config.json'
This works fine if I try to import a JavaScript file.
https://www.stefanjudis.com/snippets/how-to-import-json-files-in-es-modules-node-js/
ES modules are still reasonably new in Node.js land (they're stable since Node 14). Modules come with a built-in module system, and features such as top-level await.
I read an informative post on ES modules by Pawel Grzybek and learned that you can't import JSON files in ES modules today.
import info from `./package.json` assert { type: `json` };
const { default: info } = await import("./package.json", {
assert: {
type: "json",
},
});
That's a real bummer because I'm pretty used to doing require calls such as const data = require('./some-file.json') in Node.js.
But can you use import assertions in Node.js today?
At the time of writing, the current Node.js LTS (v18.12) still marks import assertions as experimental.
This post explains ways to deal with JSON in ES modules if you don't want to use the experimental feature yet.
Option 1: Read and parse JSON files yourself
The Node.js documentation advises to use the fs module and do the work of reading the files and parsing it yourself.
import { readFile } from 'fs/promises';
const json = JSON.parse(
await readFile(
new URL('./some-file.json', import.meta.url)
)
);
Option 2: Leverage the CommonJS require function to load JSON files
The documentation also states that you can use createRequire to load JSON files. This approach is the way Pawel advises in his blog post.
createRequire allows you to construct a CommonJS require function to use typical CommonJS features such as reading JSON in your Node.js EcmaScript modules.
import { createRequire } from "module";
const require = createRequire(import.meta.url);
const data = require("./data.json");
In TypeScript or using Babel, you can import json file in your code.
// Babel
import * as data from './example.json';
const word = data.name;
console.log(word); // output 'testing'
Reference:
https://hackernoon.com/import-json-into-typescript-8d465beded79
Importing JSON using ES modules was submitted as feature to TC39 in mid 2020, and is (at the time of this edit) in stage 3, which is the last stage before being accepted in to the spec (see https://github.com/tc39/proposal-json-modules for more details). Once landed, you will be able to use it as:
import someName from "./some/path/to/your/file.json";
Where someName is effectively the name of the variable for the JS object described by the JSON data. (And of course, note that this imports JavaScript from a JSON source, it does not "import JSON").
If you're using a modern enough bundler (like esbuild or the like) or you're using a recent enough transpiler (like babel) then you can already use this syntax without having to worry about support.
Alternatively, if you have the luxury of ownership of JSON files you can also turn your JSON into valid JS files with a minimum of extra code:
config.js
export default
{
// my json here...
}
then...
import config from '../config.js'
does not allow import of existing .json files, but does a job.
Unfortunately, ES6/ES2015 doesn't support loading JSON via the module import syntax. But...
There are many ways you can do it. Depending on your needs, you can either look into how to read files in JavaScript (window.FileReader could be an option if you're running in the browser) or use some other loaders as described in other questions (assuming you are using NodeJS).
IMO simplest way is probably to just put the JSON as a JS object into an ES6 module and export it. That way, you can just import it where you need it.
Also, worth noting if you're using Webpack, importing of JSON files will work by default (since webpack >= v2.0.0).
import config from '../config.json';
If you're using node you can:
const fs = require('fs');
const { config } = JSON.parse(fs.readFileSync('../config.json'));
OR
const evaluation = require('../config.json');
// evaluation will then contain all props, so evaluation.config
// or you could use:
const { config } = require('../config.json');
Else:
// config.js
{
// json object here
}
// script.js
import { config } from '../config.js';
OR
import * from '../config.json'
I'm using babel+browserify and I have a JSON file in a directory ./i18n/locale-en.json with translations namespace (to be used with ngTranslate).
Without having to export anything from the JSON file (which btw is not possible), I could make a default import of its content with this syntax:
import translationsJSON from './i18n/locale-en';
Depending on your build tooling and the data structure within the JSON file, it may require importing the default.
import { default as config } from '../config.json';
e.g. usage within Next.js
In a browser with fetch (basically all of them now):
At the moment, we can't import files with a JSON mime type, only files with a JavaScript mime type. It might be a feature added in the future (official discussion).
fetch('./file.json')
.then(response => response.json())
.then(obj => console.log(obj))
In Node.js v13.2+:
It currently requires the --experimental-json-modules flag, otherwise it isn't supported by default.
Try running
node --input-type module --experimental-json-modules --eval "import obj from './file.json'; console.log(obj)"
and see the obj content outputted to console.
Thanks to all the people who proposed and implemented JSON modules and Import Assertions. Since Chrome 91, you can import JSON directly, for example:
// test.json
{
"hello": "world"
}
// Static Import
import json from "./test.json" assert { type: "json" };
console.log(json.hello);
// Dynamic Import
const { default: json } = await import("./test.json", { assert: { type: "json" } });
console.log(json.hello);
// Dynamic Import
import("./test.json", { assert: { type: "json" } })
.then(module => console.log(module.default.hello));
Note: other browsers may not yet implement this feature at the moment.
A bit late, but I just stumbled across the same problem while trying to provide analytics for my web app that involved sending app version based on the package.json version.
Configuration is as follows: React + Redux, Webpack 3.5.6
The json-loader isn't doing much since Webpack 2+, so after some fiddling with it, I ended up removing it.
The solution that actually worked for me, was simply using fetch.
While this will most probably enforce some code changes to adapt to the async approach, it worked perfectly, especially given the fact that fetch will offer json decoding on the fly.
So here it is:
fetch('../../package.json')
.then(resp => resp.json())
.then((packageJson) => {
console.log(packageJson.version);
});
Do keep in mind, that since we're talking about package.json specifically here, the file will not usually come bundled in your production build (or even dev for that matter), so you will have to use the CopyWebpackPlugin to have access to it when using fetch.
Simply do this:
import * as importedConfig from '../config.json';
Then use it like the following:
const config = importedConfig.default;
Adding to the other answers, in Node.js it is possible to use require to read JSON files even inside ES modules. I found this to be especially useful when reading files inside other packages, because it takes advantage of Node's own module resolution strategy to locate the file.
require in an ES module must be first created with createRequire.
Here is a complete example:
import { createRequire } from 'module';
const require = createRequire(import.meta.url);
const packageJson = require('typescript/package.json');
console.log(`You have TypeScript version ${packageJson.version} installed.`);
In a project with TypeScript installed, the code above will read and print the TypeScript version number from package.json.
For NodeJS v12 and above, --experimental-json-modules would do the trick, without any help from babel.
https://nodejs.org/docs/latest-v14.x/api/esm.html#esm_experimental_json_modules
But it is imported in commonjs form, so import { a, b } from 'c.json' is not yet supported.
But you can do:
import c from 'c.json';
const { a, b } = c;
import data from "./resource.json”
is possible in Chrome 91.
JSON modules are now supported. This allows developers to statically import JSON instead of relying on the fetch() function which dynamically retrieves it.
https://www.stefanjudis.com/snippets/how-to-import-json-files-in-es-modules/
A more elegant solution is to use the CommonJS require function
createRequire construct a CommonJS require function so that you can use typical CommonJS features such as reading JSON
import { createRequire } from "module";
const require = createRequire(import.meta.url);
const data = require("./data.json");
importing JSON files are still experimental. It can be supported via the below flag.
--experimental-json-modules
otherwise you can load your JSON file relative to import.meta.url with fs directly:-
import { readFile } from 'fs/promises';
const config = JSON.parse(await readFile(new URL('../config.json', import.meta.url)));
you can also use module.createRequire()
import { createRequire } from 'module';
const require = createRequire(import.meta.url);
const config = require('../config.json');
I used it installing the plugin "babel-plugin-inline-json-import" and then in .balberc add the plugin.
Install plugin
npm install --save-dev babel-plugin-inline-json-import
Config plugin in babelrc
"plugin": [
"inline-json-import"
]
And this is the code where I use it
import es from './es.json'
import en from './en.json'
export const dictionary = { es, en }
I'm using
vuejs, version: 2.6.12
vuex, version: 3.6.0
vuex-i18n, version: 1.13.1.
My solution is:
messages.js:
import Vue from 'vue'
import Vuex from 'vuex';
import vuexI18n from 'vuex-i18n';
import translationsPl from './messages_pl'
import translationsEn from './messages_en'
Vue.use(Vuex);
export const messages = new Vuex.Store();
Vue.use(vuexI18n.plugin, messages);
Vue.i18n.add('en', translationsEn);
Vue.i18n.add('pl', translationsPl);
Vue.i18n.set('pl');
messages_pl.json:
{
"loadingSpinner.text:"Ładowanie..."
}
messages_en.json:
{
"loadingSpinner.default.text":"Loading..."
}
majn.js
import {messages} from './i18n/messages'
Vue.use(messages);
let filePath = '../../data/my-file.json'
let arrayImport = await import(filePath, {
assert: { type: "json" },
});
const inputArray = arrayImport.default
console.log('result', inputArray)
More information here: v8 - Dynamic import().
As said by Azad, the correct answer is to load the file with fs.readFileSync() (or any of the asynchronous variants such as fs.readFile with callback or fs.promises.readFile with promises/await, then parse the JSON with JSON.parse()
const packageJsonRaw = fs.readFileSync('location/to/package.json' )
const packageJson = JSON.parse(packageJsonRaw )
Webpack/Babel options are not practical unless you are already using that set up.
Make sure the type attribute is set to module because we are using the ES6 Modules syntax.
And here is how we would import a JSON file in our index.js file.
import myJson from './example.json' assert {type: 'json'};
import a JSON file in ECMAScript 6
import myJson from './example.json' assert {type: 'json'};
https://www.stefanjudis.com/snippets/how-to-import-json-files-in-es-modules-node-js/
ES modules are still reasonably new in Node.js land (they're stable since Node 14). Modules come with a built-in module system, and features such as top-level await.
I read an informative post on ES modules by Pawel Grzybek and learned that you can't import JSON files in ES modules today.
import info from `./package.json` assert { type: `json` };
const { default: info } = await import("./package.json", {
assert: {
type: "json",
},
});
That's a real bummer because I'm pretty used to doing require calls such as const data = require('./some-file.json') in Node.js.
But can you use import assertions in Node.js today?
At the time of writing, the current Node.js LTS (v18.12) still marks import assertions as experimental.
This post explains ways to deal with JSON in ES modules if you don't want to use the experimental feature yet.
Option 1: Read and parse JSON files yourself
The Node.js documentation advises to use the fs module and do the work of reading the files and parsing it yourself.
import { readFile } from 'fs/promises';
const json = JSON.parse(
await readFile(
new URL('./some-file.json', import.meta.url)
)
);
Option 2: Leverage the CommonJS require function to load JSON files
The documentation also states that you can use createRequire to load JSON files. This approach is the way Pawel advises in his blog post.
createRequire allows you to construct a CommonJS require function to use typical CommonJS features such as reading JSON in your Node.js EcmaScript modules.
import { createRequire } from "module";
const require = createRequire(import.meta.url);
const data = require("./data.json");
The file structure with the json extension is used to transfer data, the json file data can be retrieved locally by sending a request using the fetch command.
In the following example, the data of the count.json file is received
// count.json
fetch("./count.json")
.then((response) => { return response.json(); })
.then((data) => console.log(data));