使用循环访问嵌套对象但未定义太多？

Question

I'm working with an object literal and trying to access the nested array and iterate through a loop but it keeps displaying 59 times and 5 times again as undefined in my console but then displays the arrays. How do I stop it from doing the undefined in the console? Thanks!

var votingData = {
  candidates: [{
  name: "Harry S. Truman",
  party: "Democratic"
},
{
  name: "Thomas E. Dewey",
  party: "Republican"
},
{
  name: "Strom Thurmond",
  party: "Dixiecrat"
}]

}

for(var candidate in votingData) {
  if(votingData.hasOwnProperty(candidate)) {
    for (let i = 0, j = votingData[candidate].length; i < j; i++) {
    console.log(votingData[candidate][i].name, votingData[candidate]
    [i].party);
   }
 }
}

Answer 1

Your for/in loop is contributing to the problem as it is not needed because votingData contains only one property, candidates . Since there's just one property, you can access it directly, no need for a loop.

You only need to loop through the arrays which are in the votingData.candidates property and for that, you can either use a standard counting for loop, which you are doing or, even better, use the Array.forEach() mechanism for looping. It's better because it gives you direct access to the array element being looped over, without the need for an indexer and that allows the syntax to be much clearer, which in turn, tends to avoid bugs like this.

 var votingData = { candidates: [{ name: "Harry S. Truman", party: "Democratic" }, { name: "Thomas E. Dewey", party: "Republican" }, { name: "Strom Thurmond", party: "Dixiecrat" }], }; // Just loop through the arrays in the votingData.candidates property votingData.candidates.forEach(function(candidate) { // Now "candidate" is an object, so standard "dot notation" to access // any/all properties of the current object is the way to go. console.log(candidate.name, candidate.party); }); 

Answer 2

Your first for loop and if statement are not necessary. You're probably getting a lot of undefined because you have another property that's getting counted in the for-in statement.

Here's an example that doesn't use forEach if you prefer it.

EDIT

Formattied the data to improve readability

 var votingData = { candidates: [ { name: "Harry S. Truman", party: "Democratic" }, { name: "Thomas E. Dewey", party: "Republican" }, { name: "Strom Thurmond", party: "Dixiecrat" } ], not_candidates : [] } for (let i = 0, j = votingData.candidates.length; i < j; i++) { console.log(votingData.candidates[i].name, votingData.candidates[i].party); }