javascript - Limit JSON stringification depth

Question

When stringifying an object using JSON.stringify (or something similar) is there a way to limit the stringification depth, i.e. only go n levels deep into the object tree and ignore everything that comes after that (or better: put placeholders in there, indicating something was left out)?

I know that JSON.stringify takes a replacer function of the form function (key, value) but I didn't find a way to get the depth in the original object of the current key-value-pair handed to the replacer function.

Is there a way to do this with the default JSON.stringify implementation? Or have I reached a point where I should just implement the stringification myself? Or is there another stringification library you can recommend that has this option?

Answer 1

I wanted to stringify an object on the first level without including a third-party library / too much code.

In case you look for the same, here is a quick one-liner to do so:

var json = JSON.stringify(obj, function (k, v) { return k && v && typeof v !== "number" ? (Array.isArray(v) ? "[object Array]" : "" + v) : v; });

The top level object will have no key, so it's always simply returned, however anything that is not a "number" on the next level will be casted to a string incl. a special case for arrays, otherwise those would be exposed further more.

If you don't like this special array case, please use my old solution, that I improved, too:

var json = JSON.stringify(obj, function (k, v) { return k && v && typeof v !== "number" ? "" + v : v; }); // will expose arrays as strings.

Passing an array instead of an object in the top level will work nonetheless in both solutions.

EXAMPLES:

var obj = {
  keyA: "test",
  keyB: undefined,
  keyC: 42,
  keyD: [12, "test123", undefined]
}
obj.keyD.push(obj);
obj.keyE = obj;

var arr = [12, "test123", undefined];
arr.push(arr);

var f = function (k, v) { return k && v && typeof v !== "number" ? (Array.isArray(v) ? "[object Array]" : "" + v) : v; };
var f2 = function (k, v) { return k && v && typeof v !== "number" ? "" + v : v; };

console.log("object:", JSON.stringify(obj, f));
console.log("array:", JSON.stringify(arr, f));
console.log("");
console.log("with array string cast, so the array gets exposed:");
console.log("object:", JSON.stringify(obj, f2));
console.log("array:", JSON.stringify(arr, f2));