Value check in nested javascript object (might not exist)

Is there an elegant and concise way to avoid doing something like this to check a value deep within an object member hierarchy in javascript?

3 Answers
3

There is currently no concise way to do it in plain JavaScript, unless you use a helper function or a third-party library.

There is a proposal (at Stage 1 as of August 2018) to add the ?. operator to JavaScript which does exactly what you want.

?.

With that proposal accepted, you would be able to use ?. instead of . anywhere where a property might be missing, so your code would become:

?.

.

// careful: this syntax is not available yet
var hasDisplay = handlerInput.requestEnvelope.context?.System?.device?.supportedInterfaces?.Display


This is cheating, but you can use the _.get function from Lodash

_.get

_.get(validations, "path.to.nested.prop");


From the docs

Gets the value at path of object. If the resolved value is undefined, the defaultValue is returned in its place.

_.get

I wrote an NPM module that allows you to query by a string path.

https://www.npmjs.com/package/js-path-resolver
http://www.twelvetone.tv/docs/developer-tools/npm-modules/js-path-resolver

Here's a codepen
https://codepen.io/Flamenco/pen/xaVKjR/?editors=1111

For your use case:

import resolver from 'js-path-resolver'
const info = resolver(handlerInput, 'requestEnvelope.context.System.device.supportedInterface.Display', onError:'continue')
const hasDisplay = info.exists
const display = info.get()


In a nutshell, you split the string, then try to resolve the path, one string at a time. There are all sorts of issues implementing this, such as escaping dots, handling array indexes, etc, so using a library makes life much easier. In this library, you can also set, and delete the resolved path.

By clicking "Post Your Answer", you acknowledge that you have read our updated terms of service, privacy policy and cookie policy, and that your continued use of the website is subject to these policies.