访问Javascript JSON嵌套对象

Question

I have a json that looks like this

{
  "1": {
    "average percent match": 0.2916666667, 
    "match counts": 1.0, 
    "confidence": 0.25
  }, 
  "0": {
    "average percent match": 0.25, 
    "match counts": 1.0, 
    "confidence": 0.25 
  },
}

I tried accessing the values in the json this way.

JSON.stringify(tlist.toString("utf8"))

        for(var i = 0; i < tlist.length; i++){
        var totalCity = tlist[i]['match counts'];
        console.log(totalCity)
      } 

But i get an error that says undefined. Can anyone please point me to the problem?

Thanks you.

Answer 1

The input object is not an array (or an array like object). Hence it hasn't any property called length . It's just an object literal with key/value pairs. So you have to parse it as you would have done with every other valid json and then loop through it's keys, like below:

 var input = "{\\"1\\": { \\"average percent match\\": 0.2916666667, \\"match counts\\": 1.0, \\"confidence\\": 0.25 }, \\"0\\": { \\"average percent match\\": 0.25, \\"match counts\\": 1.0, \\"confidence\\": 0.25 } }"; var obj = JSON.parse(input); for(var key in obj){ var totalCity = obj[key]['match counts']; console.log(totalCity); } 

Update

Generally when we loop through the keys of an object, as correctly Patrick pointed out in his comment, we follow the pattern below:

for(var key in obj){
    if(obj.hasOwnProperty(key)){
        // ....
    }
}

We do need this extra check, in order to avoid enumerating the properties that are defined on the object in the prototype chain of obj . At this case, since you object is a simple object whose proto is the Object, this is not needed. This is the reason I didn't include it.

For an in depth analysis of this, please ave a look at the following links:

• https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/for...in
• https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/Object/prototype

Answer 2

That's not an array. You will have to access with it's key.

var x = {
  "0": {a: 'b'},
  "1": {a: 'b'},
}

for(key in x) {
  console.log(x[key]) //outputs {a: 'b'}
}

Answer 3

The key values in your object are string typed:

{   // Keys wrapped in "" are strings
    "1": { ... },
    "2": { ... }
}

Even though javascript is a non-strictly typed language, it still has internal types, and objects won't attempt to convert the accessing key types, they will perform a strict check on the keys to determine whether it exists. When a strict check occurs, the value is not only taken into consideration, but so is the type; it's the difference between == and === , for a === to evaluate to true both the value AND the type have to match.

But when you go to access them in your loop, you're trying to access with a number type:

// i is defined as the number 0, and incremented by 1 on each iteration
for(var i = 0; i < tlist.length; i++){
    var totalCity = tlist[i]['match counts'];
    ...
}

But don't fret, you can still keep your loop, you just need to convert i to the correct type when you're accessing your object!

for(var i = 0; i < tlist.length; i++){
    // Adding an empty string to a number will convert said number into a string
    var totalCity = tlist[i + '']['match counts'];
    ...
}

Answer 4

This will work: Please put a link to jquery, or use the script link below.

<script src="https://code.jquery.com/jquery-1.12.4.min.js"></script> 

var data = {
           "1": {
               "average percent match": 0.2916666667,
               "match counts": 1.0,
               "confidence": 0.25
           },
           "0": {
               "average percent match": 0.25,
               "match counts": 1.0,
               "confidence": 0.25
           },
       }
       var total =0;
       $.each(data, function (i, item) {
           total += item["match counts"];
       });
       alert("Total of match counts is: " + total);