I have a global list of mountains. I want to filter all French mountains. To do this, I need to check if iso3166_1Alpha2 is set to FR. The problem is that not all mountains have a value. The script dies after it hits a null value I think because this is the error:

Uncaught (in promise) TypeError: Cannot read properties of null (reading 'iso3166_1Alpha2')

This is my script. Seems my check of !== null is not working and do not know why.

function addJSON() {
  let url = ".geojson";
  fetch(url)
    .then(function (response) {
      return response.json();
    })
    .then(function (data) {
      let mtn = data.features;
      for (var i = 0; i < mtn.length; i++) {
        if (mtn[i].properties.location.iso3166_1Alpha2 !== null) {
          x = mtn[i].properties.location.iso3166_1Alpha2;
          console.log(x);
        }
      }
    });
}

I have a global list of mountains. I want to filter all French mountains. To do this, I need to check if iso3166_1Alpha2 is set to FR. The problem is that not all mountains have a value. The script dies after it hits a null value I think because this is the error:

Uncaught (in promise) TypeError: Cannot read properties of null (reading 'iso3166_1Alpha2')

This is my script. Seems my check of !== null is not working and do not know why.

function addJSON() {
  let url = "https://development.example./admin/mtn/json/mtn_areas.geojson";
  fetch(url)
    .then(function (response) {
      return response.json();
    })
    .then(function (data) {
      let mtn = data.features;
      for (var i = 0; i < mtn.length; i++) {
        if (mtn[i].properties.location.iso3166_1Alpha2 !== null) {
          x = mtn[i].properties.location.iso3166_1Alpha2;
          console.log(x);
        }
      }
    });
}

• javascript
• json

Share Improve this question Follow edited Aug 6, 2022 at 9:50 Youssouf Oumar 46.6k1616 gold badges103103 silver badges105105 bronze badges asked Aug 6, 2022 at 9:28 spreadermanspreaderman 1,08622 gold badges1414 silver badges5050 bronze badges

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1 Answer 1

Sorted by: Reset to default 2

It seems like you are getting an item that doesn't have a location property, in which case your condition won't help prevent it. Try changing your function as below. Notice I'm using Optional chaining, the ?. syntax, to avoid any null or undefined property.

function addJSON() {
  let url = "https://development.example./admin/mtn/json/mtn_areas.geojson";
  fetch(url)
    .then(function (response) {
      return response.json();
    })
    .then(function (data) {
      let mtn = data.features;
      for (var i = 0; i < mtn.length; i++) {
        if (mtn[i]?.properties?.location?.iso3166_1Alpha2) {
          x = mtn[i].properties.location.iso3166_1Alpha2;
          console.log(x);
        }
      }
    });
}