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Lodash _.defaults

Overview

The _.defaults method in lodash is used to assign properties of multiple source objects to a single target object. It takes two arguments, the first being the target object that will have the properties assigned to it and the second being the source object(s) from which the properties will be assigned.

If a property already exists on the target object, it will not be overridden by a property of the same name in a source object. Instead, the value of the existing property will be retained.

Here is an example of using _.defaults:

const defaults = { x: 1 };
const options = { y: 2 };
 
_.defaults(options, defaults);
 
console.log(options); // {x: 1, y: 2}

In the example above, we have a defaults object with a property x. We also have an options object with a property y. We pass these two objects to _.defaults with options being the target object. The _.defaults method assigns the property x from defaults to options, which did not previously exist on options.

_.defaults is useful when you have multiple objects with similar properties and you want to combine them into a single object. Rather than writing custom merge logic, you can use _.defaults to simplify your code.

Overall, the _.defaults method is a useful utility for assigning default values to an object or combining multiple objects into a single object with default and overridden values.