Computed property
A computed property is a property whose value is derived from other data when accessed rather than stored as an independent value.
Secrets of the JavaScript Ninja, Second Edition
A property whose value is derived on access or assignment rather than stored as an independent data field.
- How it is used
- Represents a value derived from object state as a property accessed through a getter and, optionally, changed through a setter.
- How deep it goes
- Explains getter concatenation and setter splitting into underlying properties, covering both reads and writes.
- Examples
- Uses a shogun’s fullTitle, derived from name and clan and assigned by splitting a title string.
- What you can do after
- Evaluate/understand how to expose derived object state as a property and map assignments back to its component properties.
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Building User-Friendly DSLs
A class property whose value is derived when accessed rather than stored as an independently assigned value.
- How it is used
- Derives a read-only rental amount for display while reflecting changes to rental price and discount inputs.
- How deep it goes
- Defines JavaScript getters, demonstrates placeholder and final formulas, and connects access to formatted JSX output.
- Examples
- Uses Rental, rentalPriceBeforeDiscount, discount, rentalPriceAfterDiscount, and a formatted rental form field.
- What you can do after
- Apply it via a JavaScript getter to derive and display a rental amount without accepting direct edits.
Read how Building User-Friendly DSLs explains computed property →
Related concepts
- accessor methodimplemented by · An accessor method or function provides access to an object's property or state by retrieving its value, assigning a value, or defining behavior for such access.
- setterimplemented by · A setter is an accessor function associated with an object property that is invoked when a value is assigned to that property.
- attributekind of · An attribute is a named property, value, or piece of information associated with an entity, object, or program element.
- getterimplemented by · A property accessor that executes code and returns a value when the property is read.
- computed property namecontrasts with · A computed property name is a syntax form in which an object or class property key is determined by evaluating an expression.
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