check if item exists in json file then get it if exists [duplicate]

I get a json file from outer link by ajax call. i want to check element is exists in this json file or not and get it if exists. because it changes every time and items increases or decreases.
If I get item and this item not existing, I get error and the code not complete. i want to check this item json.children[1].children and json.children[2].children ,….. if exists.

 {
    "num": 1,
    "name": "aa",
    "properites": [
        {
            "name": "prop1",
            "value": "value1"
        }
    ],
    "children": [
       
        {
            "num2": 1,
            "name2": "name2",
            "properites": [
                {
                    "name": "name",
                    "value": "value"
                }
            ],
            "children": []
        },
       
        {
            "name": 1,
            "num": "1",
            "attributes": [
                {
                    "name": "name",
                    "value": "value"
                }
            ],
            "children": []
        .......................... big json file