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I have a text input.

I want the user to be able to fill out a value in that text input like some of these examples:

  • results[0].address_components[0].long_name
  • results[0].formatted_address
  • fo.o[0].bar (where fo.o is a single key)
  • etc. (pretty much literally anything)

Then I want to take that value and use it as a key on some parsed JSON. So like...

$.parseJSON('data.json').results[0].address_components[0].long_name would return something like San Francisco.

How can I do this?

If I save the input value as a variable, say selector, and then try $.parseJSON('data.json')[selector] it just comes back undefined.

If I try to regex the selector and convert all instances of [ into . and remove all ] and split at . then reduce, then selectors like fo.o (one key) will break...

Thanks in advance!

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3 Answers 3

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You should generally set the results of parseJSON to a variable, rather than parse it every time you access it. parseJSON is generally going to go down to C code (depending on the environment), but it will still be really inefficient to call it over and over.

var res = $.parseJSON('data.json');

From there, you can access it like you would any other JavaScript object:

res.results, which is identical to res["results"] (which, in your case appears to be some kind of array).

A string key with special characters (., -, and pretty much anything non a-zA-Z0-9) is always accessed via the second form: res["fo.o"].

Note that this chains, so you can access res["fo.o"]["bar"] exactly as you'd address res["fo.o"].bar.

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Yeah I am assigning it to a var. I think I just posted it like that as an example. Thanks for the heads up about res["fo.o"]["bar"] working. I can probably iterate and figure it out now. =)
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I would recommend using a JavaScript library like lodash for this (if this is feasible in your project, otherwise looking at its implementation might help):

It provides a large set of utility functions. The get function does exactly what you are looking for, namely it resolves a path on an object.

Sample code (assuming _ is your lodash reference):

var path = 'results[0].address_components[0].long_name'; // the user input
var data = $.parse('data.json');
var result = _.get(data, path); // resolves the path on the data object

As for the fo.o property name, I doubt there would be an easy solution, as this essentially makes your syntax ambiguous. How would you distinguish between a property fo.o and fo?

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I suppose the trick would be to wrap fo.o in double quotes or something. I'll check into lodash, thanks! =)
That's what I was thinking too... I don't think lodash could handle that though and you'd probably have to split up the entered path in your own code first before calling the lodash get function.
Well, I've got the regex now to convert results[0].address_components[0].long_name to ["results"][0]["address_components"][0]["long_name"] but now I don't know how to combine that string with my parsed JSON... Everything I try just concatenates them together into [object Object]["results"][0]["address_components"][0]["long_name"]. console.log(parsedJSON["results"][0]["address_components"][0]["long_name"]) does work though.
To use lodash's get function, you should be able to use your original user input (as in your question, e.g. results[0].address_components[0].long_name) as the second parameter. The first parameter would be the object you obtain from $.parseJSON('data.json'). The only case you'd have to handle separately, would be the properties that contain special character such as the ..
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use eval. You would put everything as a string. So just concatenate strings based on the input. Then eval it. for example:

var str = "$.parseJSON('data.json').results[0].address_components[0].long_name";

and then eval it at runtime.

var result = eval(str);
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2 Comments

Isn't there some holy rule about not combining user input and eval?
well it seems like a programmer tool anyway. whatever works.

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