Function parameter is never for parameter to be used within JSON parse

Question

I'm going through my code and neatening it up to make it easier to understand. In my code, I parse the same JSON at different points to get different data from the JSON.
I want to create a function which I call, and pass a parameter and it will return the information from the JSON.

My JSON looks like this:

{
    "Date": "11:10:02 28-02-19",
    "Number1": 2031,
}

The function I am trying to use is this:

function dataJson(key) {
  fetch("http://file/location/data.json?newversion") // supported in modern browsers.
      .then(res => res.json()) // parses into JSON. Fails if given improper json
      .then(data => {
        return data.key;
      })
}

and I am calling it within my script like:

dataJson(Date);

It should return 11:10:02 28-02-19 but I get the error

Uncaught ReferenceError: Date is not defined

And in VS Code it tells me that key is declared but never read. When I have this in my script I would just use data.Date and it would return what I want.

How do I call the function with a parameter and pass the parameter into the JSON parse to return the data I want?

Quentin · Accepted Answer · 2019-02-28T11:26:28.137

2

Uncaught ReferenceError: Date is not defined

Date is a variable name. You need a string. "Date".

And in VS Code it tells me that key is declared but never read.

.key doesn't refer to a variable. See also: Dynamically access object property using variable

NB: dataJson has no return statement so it isn't going to return anything. See also How do I return the response from an asynchronous call?.

edited Feb 28 '19 at 11:26

answered Feb 28 '19 at 11:17

Quentin

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`dataJson` does have a return statement. `return data.key`. – JackU Feb 28 '19 at 11:19
@JackU — Wrong. That return statement belongs to the arrow function you pass to `then`. It doesn't belong to the `dataJson` function. – Quentin Feb 28 '19 at 11:19
That may be the case (which I didn't realise). However, the question was how do I pass the parameter `key` into `data.key`. – JackU Feb 28 '19 at 11:23
@JackU — See the first two paragraphs of this answer. – Quentin Feb 28 '19 at 11:23
I have taken on board your commets (I didn't understand to begin with). I am not using `data[key]`. How do I return this? If have `return` in the arrow function I get `undefined`, but if I define it as a variable and try to return outside the arrow function, I get nothing? How should I return it? – JackU Feb 28 '19 at 11:31
1

"I am not using data[key]" — Yes, that's the problem, you should be. – Quentin Feb 28 '19 at 11:33
"but if I define it as a variable and try to return outside the arrow function, I get nothing? How should I return it? " — See [How do I return the response from an asynchronous call?](https://stackoverflow.com/questions/14220321/how-do-i-return-the-response-from-an-asynchronous-call) – Quentin Feb 28 '19 at 11:34

Function parameter is never for parameter to be used within JSON parse

1 Answers1