Function reduceKeys

Calls a function for each key in an object and returns the accumulated result.

Remarks

Keys are the object's own enumerable string-keyed property names, the same as those returned by Object.keys().

Example

Basic Usage

// An empty object as the inital value:
const objectAccum = reduceKeys(
   { a: 'hello', b: 'world' },
   {},
   (accum, key, index, obj) => {
      accum // type: { a: string, b: string }
      accum[key] = obj[key].toUpperCase()
      return accum
   }
)
console.log(objectAccum) // { a: 'HELLO', b: 'WORLD' }

// The inital value does not need to be an object.
// It can be any kind, for example a number:
const numberAccum = reduceKeys(
   { a: 1, b: 2, c: 3 },
   0,
   (accum, key, index, obj) => {
      accum // type: number
      return accum + obj[key]
   }
)
console.log(numberAccum) // 6
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Custom return type

// A custom return type can be specified in two ways.
// The second method will only work with an object type
// where the inital value is an empty object ({}).

// 1. Specify a custom type using `as` on the inital value:
const strToNumAccum = reduceKeys(
   { a: '1', b: '2' },
   {} as { a: number; b: number },
   (accum, key, index, obj) => {
      accum // type: { a: number; b: number }
      obj // type: { a: string; b: string }

      const strValue = obj[key]
      accum[key] = parseInt(strValue) * 10
      return accum
   }
)
console.log(strToNumAccum) // { a: 10, b: 20 }

// 2. If the inital value is an empty object as shown above,
// you can omit it and specify the return type by overriding
// `previousValue` (accum) in the callback:
const strToNumAccum = reduceKeys(
   { a: '1', b: '2' },
   (accum: { a: number; b: number }, key, index, obj) => {
      obj // type: { a: string; b: string }
      // ... same as above
   }
)
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