It may depend on what you want to do with them. I've used this for my game, where the game engine is written in JavaScript, and the data is stored in a separate file. In this case, I just made the data file another .js file, and stored the data as one big Javascript object.
e.g.
data.js
var gameObj = {
"house": {text: "My house", directions: ["north"]},
"garden": {text: "My garden", directions: ["south", "east"]}
};
engine.js
function beginGame() {
doSomething(gameObj["house"]);
}
index.html
<head>
<script src="data.js"></script>
<script src="engine.js"></script>
</head>
You can check out an example in more detail by looking at the source of my first game (although please only use this for inspiration, don't reuse the actual code!): https://korosia.itch.io/the-witch-of-gingerglade