20 lines
602 B
Markdown
20 lines
602 B
Markdown
---
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title: defaults
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tags: object,intermediate
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---
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Assigns default values for all properties in an object that are `undefined`.
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- Use `Object.assign()` to create a new empty object and copy the original one to maintain key order.
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- Use `Array.prototype.reverse()` and the spread operator (`...`) to combine the default values from left to right.
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- Finally, use `obj` again to overwrite properties that originally had a value.
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```js
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const defaults = (obj, ...defs) =>
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Object.assign({}, obj, ...defs.reverse(), obj);
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```
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```js
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defaults({ a: 1 }, { b: 2 }, { b: 6 }, { a: 3 }); // { a: 1, b: 2 }
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```
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