I am new to typescript and learning the concepts. While playing around, I was stuck in a scenario. There is a function called functonA which basically returns an object where the input to function has a response from an API.
type Combination = ResponseType1 | ResponseType2;
interface ResponseType1 {
firstAttr: string,
thirdAttr: string
}
interface ResponseType2 {
secondAttr: string,
thirdAttr: string
}
function someCondition() {
return true // or false
}
function functionA(response: Combination) {
return {
...(someCondition()) && { first: response.firstAttr }, // true condition
...(!someCondition()) && { second: response.secondAttr }, // false condition
...{ third: response.thirdAttr } // all case
}
}
The problem here is I know that typescript can only type things based on the static analysis at build time. Initially I tried creating a type with Union of two Interfaces but failed miserably. I don't want to make fields optional in a single interface since that won't be a nice approach. API can return difference response key's based on some condition.
Now I am getting doesn't exists on type error since one of the keys is not there in other Interface.
Typescript version using: 3.0.1
Can somebody help me to find a solution for the same? please bear with me. Any help would be really appreciated.
You cannot access a property if it is not common for all types if you use a union type.
What you can here is check for property before accessing it.:
type Combination = ResponseType1 | ResponseType2;
interface ResponseType1 {
firstAttr: string,
thirdAttr: string
}
interface ResponseType2 {
secondAttr: string,
thirdAttr: string
}
function someCondition() {
return true // or false
}
function functionA(response: Combination) {
return {
...(someCondition()) && { first: ('firstAttr' in response ? response.firstAttr: undefined) }, // true condition
...(!someCondition()) && { second: ('secondAttr' in response ? response.secondAttr: undefined) }, // false condition
...{ third: response.thirdAttr } // all case
}
}
you can check the documentation here, and especially you can check the part called working with union types