Use array prototype methods recursively

Question

I'm using an infinite-level structure, similar to this:

    {
  "name": "Group1",
  "type": "group",
  "nodes": [
    {
      "name": "Node1",
      "type": "node",
      "someproperty": "somevalue1"
    },
    {
      "name": "Group2",
      "type": "group",
      "nodes": [
        {
          "name": "Node2",
          "type": "node",
          "someproperty": "somevalue2"
        },
        {
          "name": "Node3",
          "type": "node",
          "someproperty": "somevalue3"
        }
        ]
    }
    ]
}

Where we can have nodes inside groups, but also groups inside groups.

So far I've been writing recursive functions every time I need to do something, but the code is becoming quite unweildly.

I wondered if there was a way to create versions of Array.prototype methods but customise them to use recursion

e.g.to find any object (node or group) by id, I have a method

findNode(target, thisGroup) {

    if (typeof thisGroup == "undefined") {
        thisGroup = this;
    }

    // Am I the element?
    if (thisGroup.id == target) {
        return thisGroup;
    }

    // Look for element in my nodes
    var elementIx = thisGroup.nodes.findIndex(e => e.id == target);
    if (elementIx > 0) {
        // Found the element - return it
        return thisGroup.nodes[elementIx];
    }

    // Not found. Do I contain a group?
    var elementIx = thisGroup.nodes.findIndex(e => e.type == "group");

        if (elementIx > 0) {
            var nestGroup = thisGroup.nodes[elementIx];
            // If so, nest into this group and look again
            return this.findValue(target, nestGroup)
        }

    }

In the real world there's more than just Id I need to search/nest for. So how might I create my own prototype functions which I can then call like this?

thisGroup.nodes.findIndexRecursively(e => e.id == target)
thisGroup.nodes.findIndexRecursively(e => e.type=="node" && e.someProp == someValue)

what is the question about? to find (returning an object?) and/or to use a prototype of Array? where is this pointing to? maybe an instanciable or class is better for an object along with another for collections. — Nina Scholz
– Nina Scholz, Commented Mar 18, 2019 at 10:12
@NinaScholz I'm looking for a tidy way of doing recursive logic - by default the array.prototype methods like "find" and "some" do not nest / are not recursive - so I'd like to create my own prototype methods. just not sure how! — Janine Rawnsley
– Janine Rawnsley, Commented Mar 18, 2019 at 10:14
Can you give us some examples of what you really want? Something like, with this data it should return this expected output. And also whether what you want is actually needed to be in "recursive" way? — holydragon
– holydragon, Commented Mar 18, 2019 at 10:18
If you want to put methods on nodes, you could just make a nodes class that extends Array: developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/… — Scott Rudiger
– Scott Rudiger, Commented Mar 18, 2019 at 10:27
"So far I've been writing recursive functions every time I need to do something" - there's no reason to stop that. Why do you think your code is becoming unweildly? Can you show us that code? — Bergi
– Bergi, Commented Mar 18, 2019 at 11:51

Keith · Accepted Answer · 2019-03-18 10:27:33Z

2

I personally wouldn't add this to the prototype, just a simple function should do.

Here is a simple example, it makes the assumption that it's all arrays you want to recursively traverse and check.

const data = [{"name":"Group1","type":"group","nodes":[{"name":"Node1","type":"node","someproperty":"somevalue1"},{"name":"Group2","type":"group","nodes":[{"name":"Node2","type":"node","someproperty":"somevalue2"},{"name":"Node3","type":"node","someproperty":"somevalue3"}]}]}];


function rfind(arr, callback) {
  for (const a of arr) {
    const f = callback(a);
    if (f) return a;
    if (!f) {
      for (const o of Object.values(a)) {
        if (Array.isArray(o)) {
          const f2 = rfind(o, callback);
          if (f2) return f2;
        }
      }
    }
  }
}


console.log(rfind(data, f => f.name==="Node1"));
console.log(rfind(data, f => f.name==="Node3"));

answered Mar 18, 2019 at 10:27

Keith

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4 Comments

Janine Rawnsley Over a year ago

So is "callback" basically a means of passing in and using an arrow function?

Keith Over a year ago

Yes, in Javascript functions are basically objects, you can pass them around. It's not just arrow functions either, normal functions can be passed too.

Janine Rawnsley Over a year ago

What if you wanted to return all matches, not just the first? I was considering prototype methods so I can use all the proto functions but recursively (e.g. filter, map)

Keith Over a year ago

You can build an array for your results to return all matches. There are not that many Array methods, so re-implementing each one shouldn't be too hard. Not sure there is a simple way that you could say, use Array.filter, but recursively, if that's what you mean.

Nina Scholz · Accepted Answer · 2019-03-18 10:28:12Z

You could use a recursive function and seach with a callback.

function find(node, cb) {
    var result;
    if (cb(node)) return node;
    if (node.nodes) node.nodes.some(o => result = find(o, cb));
    return result;
}

var node = { name: "Group1", type: "group", nodes: [{ name: "Node1", type: "node", someproperty: "somevalue1" }, { name: "Group2", type: "group", nodes: [{ name: "Node2", type: "node", someproperty: "somevalue2" }, { name: "Node3", type: "node", someproperty: "somevalue3" }] }] },
    find1 = find(node, ({ type, someproperty }) => type === 'node' && someproperty === 'somevalue2'),
    find2 = find(node, ({ name, type }) => name === 'Group2' && type === 'group');

console.log(find1);
console.log(find2);

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