Mapping over objects

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We can map over an array, but we cannot natively map over an object. This helper function allows us to apply the same function to all properties of an object.

// we’ll use this to try and double a bunch of values in this example
const double = number => number * 2
 
// we put three numbers into an array, and also into an object as properties
const numbers = [1, 2, 3]
const coordinates = { x: 1, y: 2, z: 3 }
 
// we can `map` over an array to double all elements
numbers.map(double)
// ⇒ [2, 4, 6]
 
// we cannot `map` an object, because objects don’t have a map-function
coordinates.map(double)  // causes a TypeError
 
 
// this takes an object and a function to apply to _every_ property in it
const mapObject = (object, theFunction) => {
  // get all of the object’s keys and use `theFunction` on their values
  return Object.keys(object).reduce((result, key) => ({
    ...result,
    [key]: theFunction(object[key])
  }), {})
}
 
// `mapObject` can map all properties for us
mapObject(coordinates, double)
// ⇒ { x: 2, y: 4, z: 6 }
// we’ll use this to try and double a bunch of values in this example
const double = number => number * 2
 
// we put three numbers into an array, and also into an object as properties
const numbers = [1, 2, 3]
const coordinates = { x: 1, y: 2, z: 3 }
 
// we can `map` over an array to double all elements
numbers.map(double)
// ⇒ [2, 4, 6]
 
// we cannot `map` an object, because objects don’t have a map-function
coordinates.map(double)  // causes a TypeError
 
 
// this takes an object and a function to apply to _every_ property in it
const mapObject = (object, theFunction) => {
  // get all of the object’s keys and use `theFunction` on their values
  return Object.keys(object).reduce((result, key) => ({
    ...result,
    [key]: theFunction(object[key])
  }), {})
}
 
// `mapObject` can map all properties for us
mapObject(coordinates, double)
// ⇒ { x: 2, y: 4, z: 6 }
Debug
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