NodeJS fetch request array map returning undefined

Question

I start working with http request with NodeJS and I'm having a issue of the response returning undefined even though I check if it was not undefined.

       fetch(urlRequest, {
            method: 'post',
            body:    JSON.stringify(myJSONObject),
            headers: { 
                'Authorization': `Basic ${base64.encode(`${key.APIKey}:${key.PasswordKey}`)}`,
                'Content-Type': 'application/json'
            },
        })
        .then(res => res.json())
        .then(json => {
            // This IF validation is not working
            if(json.result.data !== undefined){
                json.result.data.map(async (myDT) => {
                    const x = myDT;
                    console.log(x);
                });
            }
        })
        .catch(err => {
            console.log(err)
        });

The code fails in the catch with the error: TypeError: Cannot read property 'data' of undefined

Why isn't the IF condition working for json.result.data?

Thanks

Dave Newton · Accepted Answer · 2020-06-08 20:31:36Z

2

The error indicates json.result is undefined, so checking for json.result.data is insufficient.

Easiest solution is:

json && json.result && json.result.data !== undefined

Depending on the rest of your environment you may be able to use null-safe navigation (?., IIRC there's a Babel for this) or something like lodash get or wrap it up in a Proxy, and so on. JS is quite malleable.

answered Jun 8, 2020 at 20:31

Dave Newton

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