Object.assign
Object.assign is a JavaScript static method that copies enumerable own properties from source objects to a target object and returns the target.
The Joy of JavaScript
Object.assign is a JavaScript built-in function that copies enumerable own properties from source objects to a target object.
- How it is used
- Composes configuration, API responses, shallow clones, and mixins by copying independent property bags into one object.
- How deep it goes
- Explains enumerability, ownership, precedence, shallow copying, and setter behavior, while stopping short of recursive cloning.
- Examples
- Uses configuration defaults, API-response merging, shallow cloning, non-enumerable properties, inherited properties, and mixin method conflicts.
- What you can do after
- Apply it to construct composed objects, merge defaults, create shallow clones, and predict conflicts between source properties.
Get Programming with JavaScript Next: New features of ECMAScript 2015, 2016, and beyond
A JavaScript static method that copies the values of enumerable own properties from one or more source objects to a target object and returns that target object.
- How it is used
- Uses Object.assign to fill default options and extend objects with additional properties.
- How deep it goes
- Works through source order, target mutation, setters, and own enumerable properties without descending into specification algorithms.
- Examples
- Uses pizza-tracking map options, enhanced spaceships, a validating setter, and an array copied into an object.
- What you can do after
- Apply it via Object.assign to set defaults, extend objects, and choose whether the original object is mutated.
Related concepts
- objectuses · A computational object is a runtime entity or structured value representing data, state, or a resource, with properties or operations defined by its programming model.
- enumerable propertyuses · An enumerable property is a JavaScript object property whose enumerable descriptor attribute determines whether it is included in property enumeration.
- setuses · A set is a collection of unique elements in which membership is determined by whether an element is present, not by duplicate occurrences.
- default valueaddresses · A default value is a predefined or automatically supplied value used when an expected input, argument, field, or configuration setting is omitted or unspecified.
- mutationcontrasts with · Mutation is an alteration to an existing value, state, data structure, or representation.
- Object.definePropertycontrasts with · Object.defineProperty is a JavaScript built-in method that creates or modifies an object property using an explicitly specified property descriptor.
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