Validation During Development Using the Salesforce CLI

Salesforce DX includes a code analysis and validation tool usable via the Salesforce CLI. Use force:lightning:lint to scan and improve your code during development. Validation using the Salesforce CLI doesn’t just help you avoid LockerService conflicts and anti-patterns. It’s a terrific practice for improving your code quality and consistency, and to uncover subtle bugs before you commit them to your codebase.

Validations using the Salesforce CLI are done separately from saving your code to Salesforce. The results are informational only. Validations performed by the Salesforce CLI fall into two categories, failures and warnings. Error messages explain both, and are displayed in your shell window. Here’s some example output:

1error     secure-document    Invalid SecureDocument API
2  Line:109:29
3  scraping = document.innerHTML;
4  ^
5  
6  warning   no-plusplus   Unary operator '++' used
7  Line:120:50
8  for (var i = (index+1); i < sibs.length; i++) {
9  ^
10  
11  error    secure-window  Invalid SecureWindow API
12  Line:33:21
13  var req = new XMLHttpRequest();
14  ^
15  
16  error  default-case  Expected a default case
17  Line:108:13
18  switch (e.keyCode) {
19  ^

Validations performed using the Salesforce CLI are different from validations performed at save time in the following important ways.

The Salesforce CLI uses many more rules to analyze your component code. Save time validations prevent you from making the most fundamental mistakes only. Validation with the Salesforce CLI errs on the side of giving you more information.
Validation via the Salesforce CLI ignores the API version of your components. Save time validations are performed only for components set to API 41.0 and later.

Lightning Components Developer Guide

Validation During Development Using the Salesforce CLI