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65 lines
1.3 KiB
65 lines
1.3 KiB
3 years ago
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# define-lazy-prop [](https://travis-ci.org/sindresorhus/define-lazy-prop)
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> Define a [lazily evaluated](https://en.wikipedia.org/wiki/Lazy_evaluation) property on an object
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Useful when the value of a property is expensive to generate, so you want to delay the computation until the property is needed. For example, improving startup performance by deferring nonessential operations.
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## Install
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```
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$ npm install define-lazy-prop
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```
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## Usage
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```js
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const defineLazyProp = require('define-lazy-prop');
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const unicorn = {
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// …
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};
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defineLazyProp(unicorn, 'rainbow', () => expensiveComputation());
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app.on('user-action', () => {
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doSomething(unicorn.rainbow);
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});
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```
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## API
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### defineLazyProp(object, propertyName, fn)
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#### object
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Type: `Object`
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Object to add property to.
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#### propertyName
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Type: `string`
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Name of the property to add.
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#### fn
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Type: `Function`
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Called the first time `propertyName` is accessed. Expected to return a value.
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## Related
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- [lazy-value](https://github.com/sindresorhus/lazy-value) - Create a lazily evaluated value
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- [import-lazy](https://github.com/sindresorhus/import-lazy) - Import a module lazily
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- [p-lazy](https://github.com/sindresorhus/p-lazy) - Create a lazy promise
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## License
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MIT © [Sindre Sorhus](https://sindresorhus.com)
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