Looping through a JSON Array gives "undefined" results

2018-06-25 00:10:07

This question already has an answer here:

Why is using “for…in” with array iteration a bad idea? 25 answers

JavaScript for…in vs for 23 answers

你忘记访问AlmostThere

  jsonData.TheArray[i].AlmostThere.whatWeAreLookingFor

for (var i = 0; i < jsonData.TheArray.length; i++) {
    console.log(jsonData.TheArray[i].AlmostThere.whatWeAreLookingFor);
}

If you loop your array TheArray in your way, the contents var will become these two objects:

{  
     "AlmostThere": {  
        "whatWeAreLookingFor":"Hello"
     }
}

and

{
    "AlmostThere": {
        "whatWeAreLookingFor":"Goodbye"
    }
}

Now you want to access the value with

contents.whatWeAreLookingFor

but this attribute is undefined for these objects. So your console logs undefined . You have to access the value with that:

contents.AlmostThere.whatWeAreLookingFor

So you get the object AlmostThere and select the attribute whatWeAreLookingFor .

If your using jquery you should use:

$.each(jsonData.TheArray, function() {
     console.log(contents.AlmostThere.whatWeAreLookingFor + '!');
});

API: http://api.jquery.com/jquery.each/

for... in iterates over the keys of an object. For an array, that means (approximately) the indexes 0 , 1 , 2 , etc.

You could use Array.prototype.forEach instead:

jsonData.theArray.forEach(function(contents) {
  console.log(contents.AlmostThere.whatWerAreLookingFor);
})

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