Check if json object is undefined in Node.js

Question

I'm getting this error "TypeError: Cannot read property '0' of undefined" when I want to extract a data from JSON file.

However, the data I want to extract is not available every time I request a JSON file, therefore, I'm getting this error which makes my Node.js Application to crash every time I'm getting this error.

Nir Levy · Accepted Answer · 2017-11-12 15:49:10Z

4

simply check if it exists or not:

if (json && json['Name'] && json['Name']['Nationality']) {
  data = json['Name']['Nationality'][0];
} else {
  // no data, do whatever error handling you want here
}

answered Nov 12, 2017 at 15:49

Nir Levy

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user1448371 · Accepted Answer · 2017-11-12 15:44:55Z

3

A solution for this sort of problem is using try-catch:

try {
  data = json['Name']['Nationality'][0];
} catch (error) {
  data = "Sorry no data found"
}

The try function is going to run the code if it did find any error it will pass it to catch.

answered Nov 12, 2017 at 15:44

user1448371

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4 Comments

Nir Levy Over a year ago

try/catch is a bit expensive here if you can simply check if it exists

user1448371 Over a year ago

I tried to do check if, but it shows me the same error even if I use check if.

user1448371 Over a year ago

BTW, may I know what you mean by "try/catch is a bit expensive", please?

Nir Levy Over a year ago

what it means is that when using try/catch what happens is that it fails, has to generate an error object (with stack and more details) and throw it for you to catch. This is more expensive to do in runtime than simply check existence

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