Traversing a JSON object in JavaScript for printing it out or applying functions/filters to every key/value - tracks the full path of every element, supports arrays, nested objects, arrays-in-arrays and objects-in-arrays

json-traverse.js

// the sample simply logs every item with its corresponding path
// replace 'logKeyValue' with custom functions/filters/... that should be applied

function traverse(obj, path = []) {
    Object.entries(obj).forEach(([key, val]) => {
        if (val !== null && typeof val == 'object') {
            if (Array.isArray(val)) {
                for (let i = 0; i < val.length; i++) {
                    let elem = val[i];
                    let itemKey = createKeyString(i, true);
                    let currentPath = Array.from(path);
                    currentPath.push(key);
                    if (elem !== null && typeof elem == 'object') {
                        currentPath.push(itemKey);
                        traverse(elem, currentPath);
                    }
                    else {
                        logKeyValue(itemKey, elem, currentPath, true);
                    }
                }
            }
            else {
                logKeyValue(createKeyString(key, false), val, path);
                let currentPath = Array.from(path);
                currentPath.push(createKeyString(key, false));
                traverse(val, currentPath);
            }
        }
        else {
            logKeyValue(createKeyString(key, Array.isArray(obj)), val, path);
        }
    });
}

function createKeyString(key, isArrayKey = false) {
    let keyVal = key;
    if (isArrayKey) {
        keyVal = '[' + keyVal + ']';
    }
    return keyVal;
}

function logKeyValue(key, val, path) {
    console.log((path.length > 0 ? (path.join('.') + '.') : '') + key + ' = ' + val);
}

const testobj = {
    'arr': [0, 0],
    'arr-in-arr': [0, 1, ['two', 'three', [4, 5, 6]]],
    'number': 123,
    'string': 'ttt',
    'parent': {
        'test': 1,
        'child': {
            'childval': 777
        },
        'array': [1, 2, 66, 9, { 'array-ob-key': 'zzz', 'array-in-array': ['a', 'b', 'c'] }, 900]
    },
    'trail': 'testtesttest'
}

traverse(testobj);

// output:
//
// arr.[0] = 0
// arr.[1] = 0
// arr-in-arr.[0] = 0
// arr-in-arr.[1] = 1
// arr-in-arr.[2].[0] = two
// arr-in-arr.[2].[1] = three
// arr-in-arr.[2].2.[0] = 4
// arr-in-arr.[2].2.[1] = 5
// arr-in-arr.[2].2.[2] = 6
// number = 123
// string = ttt
// parent = [object Object]
// parent.test = 1
// parent.child = [object Object]
// parent.child.childval = 777
// parent.array.[0] = 1
// parent.array.[1] = 2
// parent.array.[2] = 66
// parent.array.[3] = 9
// parent.array.[4].array-ob-key = zzz
// parent.array.[4].array-in-array.[0] = a
// parent.array.[4].array-in-array.[1] = b
// parent.array.[4].array-in-array.[2] = c
// parent.array.[5] = 900
// trail = testtesttest