Understanding the 'computed' Property in Vue.js

The 'computed' property in Vue.js is primarily used to calculate and return a value based on reactive dependencies within your Vue application. This distinguishes it from other properties in Vue, such as the 'methods' property used to define functions, or the 'data' property used to store the application's state.

The 'computed' property is an integral part of Vue's reactivity system. It allows developers to define properties that are used as part of the template rendering process, but whose value is not a fixed data point. Instead, that value is computed based on other reactive properties.

Let's take a look at a simple example to illustrate this:

var vm = new Vue({
  el: '#example',
  data: {
    message: 'Hello'
  },
  computed: {
    reversedMessage: function () {
      // 'this' points to the vm instance
      return this.message.split('').reverse().join('')
    }
  }
})

In this example, reversedMessage is a computed property. Its value is calculated by reversing the string of message. Whenever message changes, reversedMessage will automatically update to reflect these changes.

Compared to the data and methods properties, computed properties come in with an advantage of caching. Vue.js internally caches the results of computed properties. This means if its dependencies do not change in between renders, Vue.js will simply return the previously computed value, hence increasing performance.

However, remember to use computed properties when the values are computationally expensive or depend on other reactive properties, as they tend to be more efficient compared to methods in these instances.

The 'computed' property is a testament to Vue.js's philosophy of declarative programming, making it easier to reason about how the state of your application is changing in response to user input and other triggers.