How control javascript error when json is empty

Question

I am parsing a JSON file in javascript. Every 5 minutes the JSON is autoimatically updated with new data, during the time it is being updated the JSON is blank (for a about 2 seconds).

I get this error

Uncaught (in promise) SyntaxError: Unexpected end of JSON input at fetch.then.res

This is the code in javascript for parsing the JSON:

 fetch("http://location/file/data.json")
          .then(res => res.json()) 
          .then(data => {
            //do something
          })

How do I control this so that it doesn't flag this error? I still want an a customer error to appear using console.log(Error()).

Any help is appreciated.

Thanthu · Accepted Answer · 2019-02-28 06:19:55Z

2

This should do the trick. then() takes a second callback function as argument that receives the error object.

fetch("http://location/file/data.json")
          .then(res => res.json(), err => console.log(err)) 
          .then(data => {
            //do something
          }, err => console.log(err))

EDIT: As per comment, this way is preferred. Can read more about using promises in this link

fetch("http://location/file/data.json")
          .then(res => res.json()) 
          .then(data => {
            //do something
          })
          .catch(err => console.log(err)

edited Feb 28, 2019 at 6:19

answered Feb 27, 2019 at 12:04

Thanthu

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1 Comment

Ben Cooper Over a year ago

While this works, .catch is the canonical and proper way to log the error. In future Node versions (and likely browsers too), not having the .catch will halt execution.

ttulka · Accepted Answer · 2019-02-28 07:47:03Z

2

You can add .catch into your processing:

 fetch("http://location/file/data.json")
     .then(res => res.json()) 
     .then(data => {
         // do something
     })
     .catch(err => console.log(err.message))

EDIT: err.message instead of JSON.stringify(err).

edited Feb 28, 2019 at 7:47

answered Feb 27, 2019 at 12:04

ttulka

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2 Comments

Ben Cooper Over a year ago

Note that in a browser, the JSON.stringify isn't necessary.

ttulka Over a year ago

@BenCooper: Good point, it's a habit of mine. err.message would be maybe the best here.

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