Modify JSON

Simplest way to modify JSON files

API

Why?

Becaues I got tired of writing read/write functions for JSON files, especially when I need to change dozens of files.

Usage

• Only async use

Basic Example

Let's start with package.json file:

1// 📁package.json
2{
3    "name": "package",
4    "main": "index.js",
5    "author": "eldar",
6    "files": [ "build" ],
7    "dependencies": {
8        "type-fest": "*",
9        "fdir": ">=2"
10    }
11}

And this code:

1import { modifyJsonFile } from "modify-json-file";
2
3// modify package.json in the same dir
4await modifyJsonFile(
5    path.join(__dirname, "package.json"),
6    {
7        name: s => `super ${s}`,
8        main: "build/electron.js",
9        files: undefined, // removing the property
10        dependencies: {
11            "type-fest": "^1.0.0"
12        }
13    }
14)

After running the code, package.json will be:

1{
2    "name": "super package",
3    "main": "build/electron.js",
4    "author": "eldar",
5    "dependencies": {
6        "type-fest": "^1.0.0"
7    }
8}

As you can see above, modifyJsonFile only merges only on top level properties. Currently, there is no support for nested property merging.

Note that to simplify docs I won't use path module here, but you should use it everywhere.

In example above, modifyPackageJson should be used to provider typing for you

As always, for more usage examples you can look into test-d/index.test-d.ts or tests files.

Non-object root value

Remember, that at root level value can be any valid JSON value: string, number, boolean, null, object or array.

Be aware of modifying non object JSON files (where root type is not an object). For example:

Our code:

1import { modifyJsonFile } from "modify-json-file";
2
3// telling that root type is number (in this case it's obligatory)
4await modifyJsonFile<number>("package.json", n => n + 1);

Expected JSON:

1// 📁someNumber.json
25

Actual JSON:

1// 📁someNumber.json
2{
3    "retries": 5
4}

After running the code above, without any warnings you will get this:

1// 📁someNumber.json
2"[object Object]1"

That's because callback n => n + 1 has transformed n (object) into string.

Here, despite of the TS type (number), n is object in runtime, so n + 1 just stringified n and returned [object Object]1. Then this module just stringified the string to store output as valid JSON string in file.

Remember, this module doesn't do any type checking in runtime, you need to use typeof in callback for checking root types or schema validators (like ajv) for objects.

Formatting

By default, it will preserve tab size (thanks to detect-indent), but you can control this by overriding tabSize option. For example, we can use it to just format the file:

1import { modifyJsonFile } from "modify-json-file";
2
3// this will format file to use \t (hard tabs)
4await modifyJsonFile("someFile.json", {}, { tabSize: "hard" });

JSONC

Pass { removeJsonc: true } option to enable processing jsonc files.

WARNING, this option will remove comments and trailing commas forever!

This is temporary limitation and the option will be renamed to jsonc once limitation is removed.

modifyTsConfigJsonFile has this option enabled by default

TODO

Docs:

• Custom parser / stringifer (look at quicktype issue) to save property order

• Helper exports section

• Extend package.json typings

• Examples with immer

• Fix auto generated docs

• Runtypes?

• Describe all possible usage cases

• Give a hint, that it doesn't perform schema checking again actual file contents when type is passed into generic function modifyJsonFile

• Strip bom option

1await fs.promises.readFile(./package.json, "utf8");

Into this:

1await fs.promises.readFile(path.join(__dirname, "package.json"), "utf8");

• find a way to use FS in builder-way (like fdir does) and deprecate this module

Related

• jsonfile: simple reading / writing for json files
• immer ?

Other cool modules for working with JSON