Best Practices for Vue.js Computed Properties

What Are Computed Properties?

Imagine you have a toy that can change its color based on the temperature. If it's hot, the toy turns red; if it's cold, it turns blue. The toy's color depends on the temperature. In Vue.js, computed properties work similarly—they automatically change based on other data.

Why Use Computed Properties?

Computed properties help us keep our app's information up-to-date without doing extra work. They watch the data they depend on and update themselves when that data changes. This makes our app smarter and more efficient.

Best Practices for Computed Properties

1. Keep Computed Properties Simple

Make sure your computed properties only do one job, like counting toy cars or adding two numbers. They shouldn't try to do too many things at once.

Example:

export default {
  data() {
    return {
      numbers: [1, 2, 3, 4, 5]
    };
  },
  computed: {
    evenNumbers() {
      // Finds and returns even numbers from the list
      return this.numbers.filter(number => number % 2 === 0);
    }
  }
};        

In this example, evenNumbers looks at the list of numbers and picks out the even ones. It doesn't change the original list; it just gives us the even numbers.

2. Don't Change Computed Properties Directly

Think of computed properties like a math formula. You wouldn't change the formula itself; instead, you'd change the numbers you put into it. Similarly, to get a different result from a computed property, you change the data it uses.

Example:

export default {
  data() {
    return {
      firstName: 'Jane',
      lastName: 'Doe'
    };
  },
  computed: {
    fullName() {
      // Combines first and last name
      return `${this.firstName} ${this.lastName}`;
    }
  }
};        

Here, fullName combines firstName and lastName. To change the full name, you update firstName or lastName, not fullName.

3. Use Computed Properties for Big Tasks

If you have a task that takes a lot of time or resources, like sorting a big list, computed properties can help. They remember their results and only update when necessary, saving time and effort.

Example:

export default {
  data() {
    return {
      items: [/* a big list of items */]
    };
  },
  computed: {
    sortedItems() {
      // Sorts items by value
      return this.items.sort((a, b) => a.value - b.value);
    }
  }
};        

In this case, sortedItems organizes a big list. It only re-sorts when the original list changes, making the app run faster.

4. Avoid Doing Extra Work in Computed Properties

Computed properties should only calculate and return a value. They shouldn't do things like fetching data from the internet or changing other parts of the app.

Example:

export default {
  data() {
    return {
      message: 'Hello, Vue.js!'
    };
  },
  computed: {
    uppercasedMessage() {
      // Turns the message into uppercase letters
      return this.message.toUpperCase();
    }
  }
};        

Here, uppercasedMessage changes message to all uppercase letters without doing anything else.

5. Use Computed Properties to Describe Data Relationships

Computed properties are great for showing how different pieces of data are connected. They make your code easier to read and understand.

Example:

export default {
  data() {
    return {
      basePrice: 100,
      taxRate: 0.2
    };
  },
  computed: {
    totalPrice() {
      // Calculates the total price including tax
      return this.basePrice * (1 + this.taxRate);
    }
  }
};        

In this example, totalPrice shows how basePrice and taxRate work together to give the final price.

6. Don't Overuse Computed Properties

While computed properties are helpful, using too many can make your app complicated. Use them when you need to calculate something based on other data, but keep things simple when you can.

Example:

export default {
  data() {
    return {
      count: 0
    };
  },
  computed: {
    isEven() {
      // Checks if the count is an even number
      return this.count % 2 === 0;
    }
  }
};        

Here, isEven checks if count is an even number. This is a simple use of a computed property, but make sure not to add too many unnecessary ones.

Conclusion

By following these simple guidelines, you can make your Vue.js apps smarter and easier to manage. Computed properties help your app automatically update information, making it more efficient and fun to use.