Why Custom refs with customRef in Vue? - Purpose & Use Cases

The Big Idea

Discover how to make your reactive data smarter with just a few lines using customRef!

The Scenario

Imagine you want to track a value that changes over time and also run some extra code whenever it updates, but you have to do all this manually by watching and updating variables everywhere.

The Problem

Manually tracking changes and running extra logic is messy and repetitive. It's easy to forget to update something or write buggy code that's hard to maintain.

The Solution

Using customRef in Vue lets you create special reactive references that run your custom code automatically when the value changes, keeping your code clean and reliable.

Before vs After

✗ Before

let count = 0;
function setCount(val) {
  count = val;
  console.log('Count changed:', count);
}

✓ After

import { customRef } from 'vue';

const count = customRef((track, trigger) => {
  let value = 0;
  return {
    get() {
      track();
      return value;
    },
    set(val) {
      value = val;
      console.log('Count changed:', value);
      trigger();
    }
  };
});

What It Enables

You can create reactive values with custom behaviors that automatically run your code when they change, making your app smarter and easier to manage.

Real Life Example

Think of a form input where you want to validate the input live and show messages only when the user stops typing for a moment. customRef helps you build this debounce behavior easily.

Key Takeaways

Manual tracking of reactive values is error-prone and repetitive.

customRef lets you add custom logic to reactive references.

This makes your Vue apps cleaner, smarter, and easier to maintain.

Practice

1. What is the main purpose of using customRef in Vue?

easy

A. To create reactive references with custom get and set behavior

B. To define a component's template

C. To register global components

D. To handle lifecycle hooks automatically

Solution

1. Step 1: Understand what customRef does

   customRef allows you to create reactive references where you control how the value is read and written.

2. Step 2: Compare with other options

   Options A, C, and D relate to other Vue features, not customRef.

3. Final Answer:

   To create reactive references with custom get and set behavior -> Option A

4. Quick Check:

   customRef = custom reactive behavior [OK]

Hint: Remember: customRef customizes reactive get/set [OK]

Common Mistakes:

• Confusing customRef with component registration
• Thinking customRef manages lifecycle hooks
• Assuming customRef defines templates

2. Which of the following is the correct way to import customRef in a Vue 3 component?

easy

A. import { CustomRef } from 'vue';

B. import customRef from 'vue';

C. import { customRef } from 'vue';

D. import * as customRef from 'vue';

Solution

1. Step 1: Recall Vue 3 import syntax

   Vue exports customRef as a named export, so it must be imported with curly braces.

2. Step 2: Check each option

   import { customRef } from 'vue'; uses correct named import syntax. import customRef from 'vue'; tries default import which is incorrect. import { CustomRef } from 'vue'; uses wrong capitalization. import * as customRef from 'vue'; imports everything as an object, which is not typical for this usage.

3. Final Answer:

   import { customRef } from 'vue'; -> Option C

4. Quick Check:

   Named import uses curly braces [OK]

Hint: Use curly braces for named imports like customRef [OK]

Common Mistakes:

• Using default import instead of named import
• Wrong capitalization of customRef
• Importing everything instead of named import

3. Given the following code, what will be logged when myRef.value = 10 is called?

import { customRef } from 'vue';

const myRef = customRef((track, trigger) => {
  let value = 0;
  return {
    get() {
      track();
      return value;
    },
    set(newValue) {
      if (newValue !== value) {
        value = newValue;
        trigger();
        console.log('Value updated');
      }
    }
  };
});

myRef.value = 10;

medium

A. Value updated

B. No output

C. Error: track is not defined

D. Value updated twice

Solution

1. Step 1: Understand the set function behavior

   The set function checks if the new value differs from the current one. Since 10 !== 0, it updates value, triggers reactivity, and logs 'Value updated'.

2. Step 2: Confirm no repeated logs or errors

   There is no repeated assignment or error in the code, so only one log occurs.

3. Final Answer:

   Value updated -> Option A

4. Quick Check:

   Set logs once on value change [OK]

Hint: Set logs only when value changes [OK]

Common Mistakes:

• Expecting no output because of track confusion
• Thinking trigger causes multiple logs
• Assuming error due to track usage

4. Identify the error in this customRef implementation:

import { customRef } from 'vue';

const myRef = customRef((track, trigger) => {
  let value = 0;
  return {
    get() {
      return value;
    },
    set(newValue) {
      value = newValue;
      trigger();
    }
  };
});

medium

A. customRef cannot be used with arrow functions

B. Missing call to trigger() inside get()

C. Value should be declared with ref()

D. Missing call to track() inside get()

Solution

1. Step 1: Check get() method for reactivity tracking

   The get() method must call track() to register dependencies. Here, it returns value without calling track(), so reactivity won't work properly.

2. Step 2: Verify other parts

   Trigger is correctly called in set(). Value does not need to be a ref inside customRef. Arrow functions are allowed.

3. Final Answer:

   Missing call to track() inside get() -> Option D

4. Quick Check:

   track() needed in get() for reactivity [OK]

Hint: Always call track() inside get() [OK]

Common Mistakes:

• Forgetting to call track() in get()
• Thinking trigger() is needed in get()
• Assuming value must be a ref inside customRef

5. You want to create a customRef that debounces updates by 300ms before triggering reactivity. Which code snippet correctly implements this behavior?

hard

A. const debouncedRef = customRef((track, trigger) => {
let value;
return {
get() {
track();
return value;
},
set(newValue) {
value = newValue;
trigger();
}
};
});

B. const debouncedRef = customRef((track, trigger) => {
let value;
let timeout;
return {
get() {
track();
return value;
},
set(newValue) {
clearTimeout(timeout);
timeout = setTimeout(() => {
value = newValue;
trigger();
}, 300);
}
};
});

C. const debouncedRef = customRef((track, trigger) => {
let value;
let timeout;
return {
get() {
return value;
},
set(newValue) {
clearTimeout(timeout);
timeout = setTimeout(() => {
value = newValue;
trigger();
}, 300);
}
};
});

D. const debouncedRef = customRef((track, trigger) => {
let value;
let timeout;
return {
get() {
track();
return value;
},
set(newValue) {
value = newValue;
clearTimeout(timeout);
timeout = setTimeout(() => {
trigger();
}, 300);
}
};
});

Solution

1. Step 1: Understand debounce logic in set()

   Debounce means delaying the update and trigger until 300ms after the last set call. The correct code clears previous timeout, sets new timeout to update value and trigger after 300ms.

2. Step 2: Check get() calls track()

   The correct code calls track() in get() to register dependencies. Missing track() in get() breaks reactivity. The remaining options either lack track(), do not debounce properly, or have incorrect debouncing logic.

3. Final Answer:

   Correctly implements debounced updates with track() in get() -> Option B

4. Quick Check:

   Debounce needs clearTimeout + delayed trigger [OK]

Hint: Debounce by delaying trigger with setTimeout and clearTimeout [OK]

Common Mistakes:

• Not calling track() inside get()
• Triggering immediately without debounce
• Setting value outside timeout causing immediate update