CODEWITHSUNDEEP
javascriptjqueryjsonobject
MCSharp
MCSharp

Reputation: 1068

Function For Detecting JSON Properties In Non Existing Objects

Is there a way to check whether or not a property exists in JSON without providing a specific object?

For example,

data.programs.text.background

background is the property of text. But what if a text object does not exist in the current object?

JSON:

{
    "programs": [
        {
            "width": 500,
            "height": 600,
            "text": {
                "foreground": "black",
                "background": "white"
            }
        },
        {
            "width": 100,
            "height": 200
        },
        {
            "width": 800,
            "height": 300,
            "text": {
                "foreground": "yellow",
                "background": "red"
            }
        }
    ]
}

The console would give an error of Uncaught TypeError: Cannot read property 'background' of undefined

Testing for data.programs.text.background == undefined does not work.

Can a function be written that detects whether not the object exists and whether or not the property exists by simply providing reference to an object property such as data.programs.text.background?

Upvotes: 2

Views: 346

Answers (3)

vinayakj
vinayakj

Reputation: 5681

Use below code to find is the property present.

var data = {
    "programs": [
        {
            "width": 500,
            "height": 600,
            "text": {
                "foreground": "black",
                "background": "white"
            }
        },
        {
            "width": 100,
            "height": 200
        },
        {
            "width": 800,
            "height": 300,
            "text": {
                "foreground": "yellow",
                "background": "red"
            }
        }
    ]
}

function isPropThere(root, prop){
   var keys = prop.split(/[.,\[\]]+/);
   for(var i=1; i< keys.length; i++){

         root = root[keys[i]]
         console.dir(root)
         if(Array.isArray(root)){
          root = root[keys[++i]];
          continue;
         }
         if(!root){
                return alert('property not present');
         }
   }
 return alert('property present '+root);
}

isPropThere(data, 'data.programs[0].text.background'); // present - white
isPropThere(data, 'data.programs[1].text.background'); // not present
isPropThere(data, 'data.programs[2].text.background'); // present - red

Upvotes: 1

Halcyon
Halcyon

Reputation: 57721

Traverse the path and use Object.prototype.hasOwnProperty

function exists(object, path) {
    if (path.length === 0) {
        return true;
    }
    return Object.prototype.hasOwnProperty.call(object, path[0])
        && exists(object[path[0]], path.slice(1));
}

console.log(exists({}, [ "foo", "bar" ])); // false
console.log(exists({ "foo": { "bar": {} } }, [ "foo", "bar" ])); // true
console.log(exists({ "hasOwnProperty": { "bar": {} } }, [ "hasOwnProperty", "bar" ])); // true

// usage:

exists(data, [ "programs", "text", "background" ]);

I had another idea.

You could do:

function exists(string, context) {
    var parts = string.split("."), part;
    context = context || window;
    while (parts.length > 0) {
        part = parts.shift();
        if (Object.prototype.hasOwnProperty.call(context, part) === false) {
            return false;
        }
        context = context[part];
    }
    return true;
}

exists("data.programs.text.background");

Upvotes: 2

Danny Delott
Danny Delott

Reputation: 7008

You can use .hasOwnProperty() to determine if an object has the property on the object.

Upvotes: 2

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