在Javascript中，如何检查嵌套在另一个键/值对中的特定键/值对的存在？

Question

For example, this is the value of the object I am processing:

object = {"message":"success","dataList":{"state":"error","count":"25"}}

I know that to check if key "message" exists, I can do the following:

if(object['message']){
    //"message" exists. do stuff.
} else{
    //"message" does not exist
}

How do I check for the existence of "state" or "count" though?

Answer 1

if(object['dataList']['state']){
    // dataList["state"] exists. do stuff.
} else {
    // dataList["state"] does not exist
}

or the (in my opinion) more readable:

if(object.dataList.state){ ... }

Edit : It would also be a good idea to check for all parent objects so you will not get an unexpected error when, for example, dataList does not exist on the object:

if (object && object.dataList && object.dataList.state)

Answer 2

try like this:

object = {"message":"success","dataList":{"state":"error","count":"25"}};

    if(object.message =='success'){
        console.log(object.dataList);// your datalist object here use it
        console.log(object.dataList.state);
         console.log(object.dataList.count);
    } else{
        //"message" does not exist
    }

if you are trying to check state do this:

if(typeof(object.dataList.state) !='undefined' && object.dataList.state.length > 0){
    // dataList.state exists. do stuff.
} else {
    // dataList.state does not exist
}

Answer 3

First of all, if you are checking the existence of a property, you should use if ('message' in object) . If you use if (object['message']) , for the case object = {'message': null} , the result is wrong.

In your question, the object is nested into two layers. If there are more than two, you can try a generic solution using recursion:

function findProperty (obj, key) {
    if (typeof obj === "object") {
        if (key in obj) return true;
        var childReturned = false;
        for (k in obj) {
            childReturned = findProperty(obj[k], key);
            if (childReturned) return true;
        }
    } 
    return false;
}

var obj = {"message":"success","dataList":{"state":"error","count":"25"}};
findProperty(obj, 'message');   // => true
findProperty(obj, 'dataList');  // => true
findProperty(obj, 'state');     // => true
findProperty(obj, 'count');     // => true

Answer 4

if (object.dataList.state || object.dataList.count) {
    // ...
}