Username Availability with an Asynchronous Validator in Angular

A little while ago I released an article named Advanced Forms & Validation in Ionic where we discussed the concept of using Validators that Angular provides for validating form fields. These validators come in two flavours: synchronous and asynchronous. Synchronous validators can be used to perform simple synchronous checks like whether a field is empty, whether it exceeds a maximum length, or whether it matches a regex pattern. Asynchronous validators can perform more complex validations that can't be run synchronously, like hitting a server to check the availability of a username or email. If you do not understand the difference between synchronous and asynchronous code, I would recommend watching this video first. A form that uses this functionality might be built using Angular's FormBuilder like this: this.myForm = formBuilder.group({ firstName: ['value'], lastName: ['value', *validation function goes here*], age: ['value', *validation function goes here*, *asynchronous validation function goes here*] }); I've already explained most of how this works in the previous tutorial, however, a lot of people said that they had difficulty getting the validators to work when making a request to a real server (the previous tutorial just makes a "fake" asynchronous request to a server).

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