Class and style binding conditionally in Vue JS | Vue Binding
A common need for data binding is manipulating an element’s class list and its inline styles. Since they are both attributes, we can use v-bind to handle them: we only need to calculate a final string with our expressions. However, meddling with string concatenation is annoying and error-prone. For this reason, Vue provides special enhancements when v-bind is used with class and style. In addition to strings, the expressions can also evaluate to objects or arrays.