• Dart

Map x = json.jsonDecode(await new File('data.json').readAsString());

• Dart

Map x = json.jsonDecode(new File('data.json').readAsStringSync());

• Clojure

(def x (read-value (file "data.json")))

• C#

JObject x = JObject.Parse(File.ReadAllText("data.json"));

• D

JSONValue x = "data.json".readText.parseJSON;

struct User {
    int age;
    string name;

    this(JSONValue user) {
        age  = user["age"];
        name = user["name"];
    }
}

auto user = User(x);

• Elixir

defmodule JsonTest do
  def get_json(filename) do
    with {:ok, body} <- File.read(filename),
         {:ok, json} <- Poison.decode(body), do: {:ok, json}
  end
end

x = JsonTest.get_json("data.json")

• Go

r, err := os.Open(filename)
if err != nil {
	return err
}
decoder := json.NewDecoder(r)
err = decoder.Decode(&x)
if err != nil {
	return err
}

• Go

buffer, err := os.ReadFile("data.json")
if err != nil {
	return err
}
err = json.Unmarshal(buffer, &x)
if err != nil {
	return err
}

• JS

const x = JSON.parse(fs.readFileSync('./data.json'));

• JS

const x = require('./data.json');

• Lua

file = io.open("data.json")
x = cjson.decode(file:read("a"))
file:close()

• PHP

$x = json_decode(file_get_contents('data.json'));

• Perl

my $str = read_file('data.json');
my $x = decode_json($str);

• Python

with open("data.json", "r") as input:
    x = json.load(input)

• Ruby

x = JSON.parse(File.read('data.json'))

• Rust

let x = ::serde_json::from_reader(File::open("data.json")?)?;