CODEWITHSUNDEEP
typescript
Pedro Ferrari
Pedro Ferrari

Reputation: 323

How to properly iterate through an Object in TypeScript

I am trying to figure out a proper way to loop through an Object while using TypeScript. The following examples would be valid JavaScript but I do understand why it becomes a problem in TypeScript, however I am not finding the correct way to proceed with this task and I was wondering if I am thinking wrong about it.

My goal is to iterate through a two-level-deep Object and be able to access the item directly from the Object at the end, and not only its value.

Example:

interface A {
  abc: number
  acd: number
}
interface B {
  bcd: number
  bde: number
}
interface C {
  cde: number
  cef: number
}
interface Data {
  a: A
  b: B
  c: C
}

const data: Data = {
  a: {
    abc: 1,
    acd: 2
  },
  b: {
    bcd: 3,
    bde: 4
  },
  c: {
    cde: 5,
    cef: 6
  }
}

// Trying with for-in
for (const cat in data) {
  for (const item in cat) {
    console.log(cat, item) // works just fine cause both are strings
    console.log(data[cat][item]) // both cat and items are strings and not keys of Data.
  }
}

// Trying with for-of
for (const cat of Object.keys(data)) {
  for (const item of Object.keys(cat)) {
    console.log(data[cat][item]) // Same, cat becomes just a string and not valid key of Data.
  }
}

// Trying with forEach
Object.keys(data).forEach((cat) => {
  Object.keys(cat).forEach(item => console.log(data[cat][item])) // same thing, cat is just a string and not exactly a key of Data
})

Thank you all :)

Upvotes: 0

Views: 95

Answers (3)

CharlesRA
CharlesRA

Reputation: 395

See this:

for (let key of Object.keys(data.a)) {
   console.log(data.a[key]);

This will log out all the keys of data.a. You could do anything to each key by performing this loop through the keys and accessing those key values with data.a[key].

Upvotes: 0

Raji Hawa
Raji Hawa

Reputation: 156

I hate to use the "any" but in this code snippet i think its pretty safe to use duo to the if statments


Object.keys(data).forEach((key1 ) => {
    if(key1 in data) {
        Object.keys((data as any)[key1]).forEach((key2) => {
            if(key2 in (data as any)[key1]) {
                console.log((data as any)[key1][key2])
            }

        })
    }  
})

Upvotes: 1

falinsky
falinsky

Reputation: 7428

When you're iterating via Object.keys(someObject) - you're retrieving keys, not objects.

for (let catKey of Object.keys(data)) {
  for (let itemKey of Object.keys(data[catKey])) {
    console.log(catKey, itemKey)
    console.log(data[catKey][itemKey])
  }
}

Upvotes: 2

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