TypeScript - Loop return gets skipped and base condition is returned

Marios Yiannakou 0
Viewed 35

I have a custom object that is defined as following (names and properties have been simplified to avoid confidential information leakage):

type T = {
  id: number;
  title: string;
};

This type is used to create a list of Ts like so:

const IT: StringMap<T> = {
  a: {
    id: 0,
    title: 'foo',
  },
  b: {
    id: 1,
    title: 'bar',
  },
  c: {
    id: 2,
    title: 'foobar',
  },
}

I need a way to be able to retrieve one of these T type objects based on their id. So I created the following function:

const getTUsingId = (ts: StringMap<T>, id: number): T => {
  Object.values(ts).forEach((t: T) => {
    if (t.id === id) {
      return t
    }
  });

  // This is as a safeguard to return a default value in case an invalid id is passed
  return ts['a'] 
}

For whatever reason, this function will always return ts['a'] regardless of what id I pass to it. Console logging t.id === id even returns true but it still carries on until the end of the ts map!

Any help is highly appreciated!

function for-loop typescript javascript
2 Answers

return won't break out of your loop. You need to use a plain for loop:

const getTUsingId = (ts: StringMap<T>, id: number): T => {
  for (const t of Object.values(ts)) {
    if (t.id === id) {
      return t
    }
  }

  return ts['a'] 
}
caTS0

the forEach callback is for performing an action on every element in the array, it's return isn't used for termination, what you want is filter, find or a regular for loop

Object.values(ts).filter((t: T) => {
  return t.id === id;
});

return all values where the id matches as a fresh array, you would use this if there was a possibility of multiple match, you would then need to parse the returned array to decide which match was correct

Object.values(ts).find((t: T) => {
  return t.id === id;
});

return only the first matching value

for(const t of Object.values(ts))
  if (t.id === id) {
    return t
  }
});

my preference would be find

const getTUsingId = (ts: StringMap<T>, id: number): T => {
  return Object.values(ts).find((t: T) => t.id === id) ?? ts['a'] 
}
userVs530
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