how to iterate over nested array object in javascript

Question

I would like to know how to iterate through a nested array of objects in Javascipt? I have a sample object named obj. I want to retrieve the object based on condition 'in' is 'string' and 'out' 'number'.

// tried got stuck
const output = [];
    myList.forEach(entry => {
      Object.keys(entry).forEach(key => {
        const entity = entry[key][0];
        if (entity.in === "string" && entity.out === "number") {
          output.push(entity);
        }
      });
    });

var obj = [{
    "ston": [{
      "id": "identity1",
      "in": "string",
      "out": "number",
      "value": 10
    },{
        "id": "identity2",
        "in": "string",
        "out": "number",
        "value": 10
    }],
    "nton": [{
      "id": "identity1",
      "in": "number",
      "out": "number",
      "value": 20
    },{
      "id": "identity2",
      "in": "number",
      "out": "number",
      "value": 30
    }]
  }]

Expected Output

   [{
      "id": "identity1",
      "in": "string",
      "out": "number",
      "value": 10
    },{
        "id": "identity2",
        "in": "string",
        "out": "number",
        "value": 10
    }]

Answer 1

Here you have one solution that uses mainly Array.reduce() to iterate over the outter objects of the array, get a flattened array of the values from every outter object to create an array with inner objects and then filter those meeting the condition while saving they in a new array:

var obj = [
  {
    "ston": [
      {"id": "identity1", "in": "string", "out": "number", "value": 10},
      {"id": "identity2", "in": "string", "out": "number", "value": 10}
    ],
    "nton": [
      {"id": "identity1", "in": "number", "out": "number", "value": 20},
      {"id": "identity2", "in": "number", "out": "number", "value": 30}
    ]
  }
];

let res = obj.reduce((acc, o) =>
{
    acc = acc.concat(Object.values(o).flat().filter(
        o => o.in === "string" && o.out === "number"
    ));
    return acc;
}, []);

console.log(res);

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Other documentation of used methods:

• Array.concat()
• Array.flat()
• Array.filter()
• Object.values()

Or, after some time thinking, you can use the next simplified version with Array.map()

var obj = [
  {
    "ston": [
      {"id": "identity1", "in": "string", "out": "number", "value": 10},
      {"id": "identity2", "in": "string", "out": "number", "value": 10}
    ],
    "nton": [
      {"id": "identity1", "in": "number", "out": "number", "value": 20},
      {"id": "identity2", "in": "number", "out": "number", "value": 30}
    ]
  }
];

let res = obj.map(Object.values).flat(2).filter(
    o => o.in === "string" && o.out === "number"
);

console.log(res);

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Answer 2

You can use rebuild that object to a nested array then flatten and finally filter.

var obj = [
  {
    "ston": [
      {"id": "identity1", "in": "string", "out": "number", "value": 10},
      {"id": "identity2", "in": "string", "out": "number", "value": 10}
    ],
    "nton": [
      {"id": "identity1", "in": "number", "out": "number", "value": 20},
      {"id": "identity2", "in": "number", "out": "number", "value": 30}
    ]
  }
];

const tmp = obj.map(e => Object.entries(e).map(([k, v]) => v)).flat(3)

const rs = tmp.filter(e => e.out==='number' && e.in ==='string')

console.log(rs)

Answer 3

Simple recursive function:

var obj = [{
  "ston": [{
    "id": "identity1",
    "in": "string",
    "out": "number",
    "value": 10
  }, {
    "id": "identity2",
    "in": "string",
    "out": "number",
    "value": 10
  }],
  "nton": [{
    "id": "identity1",
    "in": "number",
    "out": "number",
    "value": 20
  }, {
    "id": "identity2",
    "in": "number",
    "out": "number",
    "value": 30
  }]
}];

function getObjects(inVal, outVal) {
  var matches = [];
  obj.forEach(child => {
    Object.values(child).forEach(arr => {
      if (arr.some(e => e.in == inVal && e.out == outVal)) {
        matches.push([...arr.filter(e => e => e.in == inVal && e.out == outVal)]);
      }
    });
  });
  return matches.flat();
}

console.log(getObjects("string", "number"));