Tutorials

Lodash _.mergeWith() Object Method

Posted in lodash Tutorial

Updated on Mar 14, 2024

By Mari Selvan

👁️ 44 - Views

⏳ 4 mins

💬 1 Comment

Photo Credit to CodeToFun

🙋 Introduction

In the realm of JavaScript development, managing complex objects and their merging operations can be challenging. Enter Lodash, a powerful utility library that offers a plethora of functions to simplify object manipulation. Among these functions lies the _.mergeWith() method, a versatile tool for merging two or more objects while allowing customization through a provided customizer function.

This method enhances code flexibility and maintainability, making it indispensable for developers dealing with nested or conflicting data structures.

🧠 Understanding _.mergeWith() Method

The _.mergeWith() method in Lodash is designed to merge two or more objects into a single object while allowing developers to define custom merging behavior. This customizability is achieved through a provided customizer function, which enables precise control over how conflicting properties are resolved during the merge operation.

💡 Syntax

The syntax for the _.mergeWith() method is straightforward:

syntax.js

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_.mergeWith(object, sources, customizer)

object: The destination object to merge into.
sources: The source objects to merge from.
customizer: The function invoked to customize merging behavior.

📝 Example

Let's dive into a simple example to illustrate the usage of the _.mergeWith() method:

example.js

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const _ = require('lodash');

const targetObject = {
  a: {
    value: 1,
    details: {
      type: 'number'
    }
  },
  b: {
    value: 2,
    details: {
      type: 'number'
    }
  }
};

const sourceObject = {
  a: {
    value: 3
  },
  b: {
    details: {
      description: 'This is object b'
    }
  },
  c: {
    value: 4
  }
};

function customizer(objValue, srcValue, key, object, source) {
  if(_.isObject(objValue)) {
    return _.mergeWith(objValue, srcValue, customizer);
  }
  return srcValue;
}

const mergedObject = _.mergeWith(targetObject, sourceObject, customizer);

console.log(mergedObject);

In this example, the targetObject and sourceObject are merged using _.mergeWith(), with a customizer function customizer() provided to customize the merge behavior. The result is stored in mergedObject, where conflicting properties are resolved according to the logic defined in the customizer function.

🏆 Best Practices

When working with the _.mergeWith() method, consider the following best practices:

Understand Customizer Function:

Familiarize yourself with the customizer function provided to _.mergeWith(). This function allows you to define how conflicting properties should be merged, providing granular control over the merge operation.
example.js
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```
function customizer(objValue, srcValue, key, object, source) {
  if(_.isObject(objValue)) {
    return _.mergeWith(objValue, srcValue, customizer);
  }
  return srcValue;
}
```
Handle Nested Objects:

Ensure that your customizer function can handle nested objects appropriately. This is crucial for scenarios involving deeply nested data structures where conflicts may occur at multiple levels.
example.js
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```
function customizer(objValue, srcValue, key, object, source) {
  if(_.isObject(objValue)) {
    return _.mergeWith(objValue, srcValue, customizer);
  }
  return srcValue;
}
```
Test with Various Scenarios:

Thoroughly test your merge operations with a variety of scenarios, including different object structures and customizer functions. This ensures that your merging logic behaves as expected across different use cases.
example.js
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```
const object1 = {
  a: {
    b: 1
  }
};

const object2 = {
  a: {
    c: 2
  }
};

const mergedObject = _.mergeWith(object1, object2, (objValue, srcValue) => objValue + srcValue);

console.log(mergedObject);
// Output: { a: { b: 1, c: 2 } }
```

📚 Use Cases

Resolving Conflicts in Object Merging:

_.mergeWith() is particularly useful when merging objects with conflicting properties, allowing developers to define custom resolution strategies for handling these conflicts.

example.js

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const targetObject = { a: { value: 1 } };
const sourceObject = { a: { value: 2 } };

const mergedObject = _.mergeWith(targetObject, sourceObject, (objValue, srcValue) => objValue + srcValue);

console.log(mergedObject);
// Output: { a: { value: 3 } }

Customized Merging Logic:

In scenarios where standard merging behavior is insufficient, _.mergeWith() empowers developers to implement custom merging logic tailored to their specific requirements.

example.js

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const targetObject = { a: { value: 1 } };
const sourceObject = { a: { value: 2 } };

function customizer(objValue, srcValue) {
    return objValue * srcValue;
}

const mergedObject = _.mergeWith(targetObject, sourceObject, customizer);

console.log(mergedObject);
// Output: { a: { value: 2 } }

Deeply Nested Object Merging:

For scenarios involving deeply nested objects, _.mergeWith() provides a convenient solution for merging complex data structures while preserving the integrity of nested properties.

example.js

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const targetObject = { a: { b: { c: 1 } } };
const sourceObject = { a: { b: { d: 2 } } };

const mergedObject = _.mergeWith(targetObject, sourceObject, (objValue, srcValue) => objValue + srcValue);

console.log(mergedObject);
// Output: { a: { b: { c: 1, d: 2 } } }

🎉 Conclusion

The _.mergeWith() method in Lodash offers a powerful solution for merging objects with customizable merging behavior. Whether you need to resolve conflicts, implement custom merging logic, or handle deeply nested data structures, _.mergeWith() provides the flexibility and control required for efficient object manipulation in JavaScript.

By adhering to best practices and exploring diverse use cases, you can harness the full potential of the _.mergeWith() method in your Lodash projects.