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ES2020 Optional Chaining & Nullish Coalescing

Wednesday, March 11th, 2020

Of the various Features proposed in ES2020, perhaps two of the simplest features will prove to be the most useful, at least in terms of simplification and maintenance are concerned.

Specifically, the Optional Chaining Operator and Nullish Coalescing Operator are of particular interest as they are certain to result in less verbose, less error prone expressions.

Optional Chaining

In a nutshell, Optional Chaining provides a syntax for undefined / null checks when performing nested object references using a simple question mark appended by a dot (?.) notation.

For instance, consider how many times you may have written defensive expressions similar to the following:

Or perhaps you have assigned intermediate values to temporary variables to perform the same:

The need to check for possible reference errors quickly becomes tedious, and with each lookup we increase the potential for introducing bugs. Utilities can be implemented for delegating these checks, but ultimately, this just moves the problem from one context to another, resulting in additional points for failure.

With Optional Chaining, however, accessing properties safely becomes considerably less verbose, as the examples above can be simplified to:

Reference checks when invoking functions also become simplified:

And dynamic property references can safely be performed as well:

Nullish Coalescing

In addition, combined with the Nullish Coalescing Operator, Optional Chaining becomes even more succinct as one can specify a value to resolve to rather than the default (undefined) by simply using a double question mark (??) notation. For example:

Moreover, Nullish Coalescing, while intended as a compliment to Optional Chaining, also solves additional problems when dealing with falsy values. For instance, consider how many times you may have written something similar to the following:

With the Nullish Coalescing Operator, we can avoid the problems outlined above as only undefined and null values will evaluate to true, so falsy values are safe:

Since Nullish Coalescing only checks for undefined and null, the above holds true for all other falsy values, so false, empty strings, and NaN are safe as well..

Optional Chaining w/Destructuring

One thing to note is that Optional Chaining does not resolve when destructuring. So, for example, the following will throw an exception:

Interestingly, though, combined with Nullish Coalescing, an exception will not be raised; though, the default will not be assigned, either:

Conclusion

As can be seen, ES2020 has no shortage of new features on offer to be excited about and, while arguably not as exciting as other features, Optional Chaining combined with Nullish Coalescing will certainly prove to be valuable additions.

Both Optional Chaining and Nullish Coalescing proposals are currently at Stage 4 and are available in most modern browsers as well as via @babel/plugin-proposal-optional-chaining and @babel/plugin-proposal-nullish-coalescing-operator.

Quick Tip: React Spring & Babel Loader

Thursday, October 3rd, 2019

Recently, I had integrated React Spring within an Application, and while it is one of the best Animation Libraries for React I have come across in quite some time; unfortunately, I encountered some issues when running tests and production builds.

Essentially, the issues I experienced were related to the imported modules being written in ES6. This was an issue for me as I prefer to have webpack babel-loader configured to exclude node_modules and only transpile project sources.

Fortunately, the work around for this is quite simple: just import the CommonJS modules (i.e. .cjs extensions) rather than their ES6 counterparts (i.e. no extension).

Thus, simply changing:

To:

Resolves the issue.

And so, should you happen to come across build issues when using React Spring, a nice alternative to including the node_modules directory or specific dependencies is to simply import the CommonJS modules.

React-Bootstrap ES6 Imports

Friday, August 12th, 2016

When leveraging React Bootstrap, one important consideration missing from the documentation (or perhaps, simply not emphasized enough) relates to module access when using ES6 imports.

Specifically, in the context of React Bootstrap’s “convenience components” <Component.SubComponent> (e.g. <Modal.Body>), such imports must be made explicit as they can not be resolved against their parent components during transformations of ES6 imports to CommonJS modules.

For instance, one can not reference sub-components as follows:

During transpilation, the above reference will result in Babel (specifically, the babel-plugin-transform-es2015-modules-commonjs module) causing an upstream exception:

Property object of JSXMemberExpression expected node to be of a type [“JSXMemberExpression”,”JSXIdentifier”] but instead got “MemberExpression

Fortunately, the solution to the issue is rather straight-forward; simply import the sub-component explicitly via react-bootstrap/lib , for example:

With the above example, the previous conversion errors will be resolved, and all will be well again.

Overall, I actually prefer the explicit imports (though it would be more convenient if they were exported via ‘react-bootstrap’).

And so, for the time being, a minor nuance worth noting should you find yourself trying to diagnose this issue at some point.

IIFE in ES6

Wednesday, April 6th, 2016

TL;DR: In ES6, an IIFE is implemented as follows:


Unlike ES5, which is syntactically less opinionated, in ES6, when using an IIFE, parenthetical order matters.

For instance, in ES5 an IIFE could be written either as:

or

As can be seen in the above examples, in ES5 one could either wrap and invoke a function expression in parentheses, or wrap the function expression in parentheses and invoke the function outside of the parentheses.

However, in ES6, the former throws an exception, thus, one can not use:

But rather, the invocation must be made outside of the parentheses as follows:

As an aside for those who are curious, the syntax requirements are specific to ES6 and not a by-product of any particular transpilers (i.e. Babel, Traceur, etc.).