Lodash _.assignIn() Method

Syntax, Parameter and Return Value

Syntax:

_.assignIn(target, ...sources)

Parameters:

• target (Object): The destination object.
   
• ...sources (Object): The source objects.

Return Value: 

(Object) - Returns the modified target object.

Examples 

Merging Inherited Properties:

• JavaScript

JavaScript

var _ = require('lodash');

function Parent() {

  this.inheritedProperty = 'inherited';

}

Parent.prototype.parentMethod = function() {};

var childObject = new Parent();

var sourceObject = { ownProperty: 'own' };

_.assignIn(childObject, sourceObject);

console.log(childObject); 

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Output: 

{ inheritedProperty: 'inherited', ownProperty: 'own' }

Demonstrates _.assignIn() merging both own and inherited properties.

Combining Multiple Objects:

• JavaScript

JavaScript

var defaults = { a: 1, b: 2 };

var additionalProps = { b: 3, c: 4 };

var inheritedProps = Object.create({ d: 5 });

var result = _.assignIn({}, defaults, additionalProps, inheritedProps);

console.log(result); 

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 Output: 

{ a: 1, b: 3, c: 4, d: 5 }

Shows merging properties from multiple sources, including inherited ones.

Extending an Object with Prototype Properties:

• JavaScript

JavaScript

var base = { method1: function() {} };

var derived = Object.create(base);

derived.ownMethod = function() {};

var extended = _.assignIn({ newProp: 'value' }, derived);

console.log(extended.hasOwnProperty('method1')); 

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Output: 

true

An example of extending an object with properties from another object that has prototype methods.

Assigning Functions and Properties Together:

• JavaScript

JavaScript

var target = {};

var source1 = { prop: 'value' };

function source2() { this.func = function() {}; }

_.assignIn(target, source1, new source2());

console.log(target); 

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Output: 

{ prop: 'value', func: [Function] }

Demonstrates using _.assignIn() to combine properties and functions from different sources into a single object.

Frequently Asked Questions

How does _.assignIn() differ from _.assign()?

While _.assign() copies only the object's own properties, _.assignIn() copies both own and inherited properties from the prototype chain.

Does _.assignIn() perform deep cloning?

No, similar to _.assign(), _.assignIn() performs a shallow copy. It does not clone nested objects but copies their references.

Is _.assignIn() safe to use with all objects?

Caution is advised when using _.assignIn(), especially with objects that have a complex prototype chain, as it might lead to unintended side effects due to copying inherited properties.

Conclusion

Lodash's _.assignIn() method is a versatile tool for merging both own and inherited properties from source objects into a target object. It is especially useful in object-oriented programming where extensions and mixins are common, providing a straightforward approach to combine behaviors and properties from multiple objects.

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