ES6's "Computed Property Names" feature allows you to have an expression (a piece of code that results in a single value like a variable or function invocation) be computed as a property name on an object.

For example, say you wanted to create a function that took in two arguments (key, value) and returned an object using those arguments. Before Computed Property Names, because the property name on the object was a variable (key), you'd have to create the object first, then use bracket notation to assign that property to the value.

function objectify (key, value) {
  let obj = {}
  obj[key] = value
  return obj
}


objectify('name', 'Tyler') // { name: 'Tyler' }

However, now with Computed Property Names, you can use object literal notation to assign the expression as a property on the object without having to create it first. So the code above can now be rewritten like this.

function objectify (key, value) {
  return {
    [key]: value
  }
}


objectify('name', 'Tyler') // { name: 'Tyler' }

Where key can be any expression as long as it's wrapped in brackets, [].

Before you leave

I know, another newsletter pitch - but hear me out. Most JavaScript newsletters are terrible. When's the last time you actually looked forward to getting one? Even worse, when's the last time you actually read one? We wanted to change that.

We call it Bytes, but others call it their favorite newsletter.

Delivered to 111,963 developers every Monday and Thursday