CODEWITHSUNDEEP
javascriptarraysjsonnode.js
danielgoba84
danielgoba84

Reputation: 13

Error while trying to iterate JSON array in JavaScript

I have JSON file, which i load in js code without problems using JSON.parse() (A reduced example of the file shown here, it's 25 items long):

{
    "List": [
    {  "Term": "Tos"   },
    {  "Term": "Gripa" },
    {  "Term": "Catarro"}, 
    {  "Term": "Flemas"}
    ]
}

When I iterate it accessing one item per iteration I have no problems, but when i try to increase the index to access to items per iteration it throws the following error (Comment in code shows the line with the problem):

console.log(searchTerms[j].Term);

TypeError: Cannot read property 'Term' of undefined

var data = fs.readFileSync(searchTermsFile);
var searchTerms = JSON.parse(data);
searchTerms = searchTerms.List;
for(var j=0;j<searchTerms.length;j+=4)
{
    console.log(searchTerms[j].Term);
    j+=1;
    console.log(searchTerms[j].Term); /****<---- THIS LINE THROWS THE ERROR ****/
}

Upvotes: 1

Views: 504

Answers (5)

Yashar Aliabbasi
Yashar Aliabbasi

Reputation: 2719

Your object contains 4 Term and your for loop count to 4 but j+=1 in last iteration make j=5 and there is no object in searchTerms[5].This is why your code doesn't work. I write sample program.I hope this helps you:

var data = {
    "List": [
        {"Term": "1"},
        {"Term": "2"},
        {"Term": "3"},
        {"Term": "4"},
        {"Term": "5"},
        {"Term": "6"},
        {"Term": "7"},
        {"Term": "8"},
        {"Term": "9"},
        {"Term": "10"},
        {"Term": "11"},
        {"Term": "12"}
    ]
};

function test() {
  var searchTerms = data.List;
  var j = 0;
  var currentFiveObject = [];
  for (j = 0; j < searchTerms.length; j += 5) {
    currentFiveObject = [];
    for (var i = 0; i < 5; i++) {
      if (j + i < searchTerms.length)
        currentFiveObject.push(searchTerms[j + i])
      else
        break;
    }
    console.log(currentFiveObject);
  }
}
test();

Upvotes: 1

Nina Scholz
Nina Scholz

Reputation: 386600

You could use a default object, which resolves the error, but returns undefined as well.

j += 1;
console.log((searchTerms[j] || {}).Term);

The other way to deal with indices out of range, is to use a check in advance and prevent from using an index greater than the last index value.

if (j < searchTerms.length) {
    // process item
    console.log(searchTerms[j].Term);
}

Upvotes: 0

Armando Mart&#237;nez
Armando Mart&#237;nez

Reputation: 11

The real problem you're facing is that your j-index is requiring an item that's not contained in your JSON object. I found no reason for your cycle to increase your index variable in the middle of logging your Terms.

If that index increment is intended, then you need to consider if the value of j is equal or larger than searchTerms length before using it as the index accessor.

Remove it or deal with it.

Upvotes: 0

Gohel Dhaval
Gohel Dhaval

Reputation: 820

You can try this

var data = fs.readFileSync(searchTermsFile);
var searchTerms = JSON.parse(data);
var i = 0;
searchTerms = searchTerms.List;for(var j=0;j<searchTerms.length;j++)
{
 i = j
 console.log((searchTerms[i] || {}).Term);
 i +=1;
 console.log((searchTerms[i] || {}).Term); 
}

Upvotes: 0

Shubham Khatri
Shubham Khatri

Reputation: 281726

Thats because you are incrementing j and then checking , however since you are iterating till the length - 1 it will go out of bounds after j += 1, try

var data = fs.readFileSync(searchTermsFile);
var searchTerms = JSON.parse(data);
searchTerms = searchTerms.List;for(var j=0;j<searchTerms.length - 1;j++)
{
 console.log(searchTerms[j].Term);
 j+=1;
 console.log(searchTerms[j].Term); 
}

Upvotes: 0

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