I have variable with a type as
let campaigns : {
[key: string] : string[]
} | string[] = []
As we can see in a logic variable is either one or another type. When I know for sure in my logic that is an array I will try to use as campaigns.push("string"). But I will get Typescript error as saying that you can't use push on object, cause typescript doesn't know that in my logic I illuminated a chance on been an object. How let Typescript know that campaign.push() is a legal operation ?
please do like this:
const arrOrObj: Record<string, string> | string[] = []
if (Array.isArray(arrOrObj)) arrOrObj.push("a")
Or you can use a type checking function:
function isArrayString(arr: object): arr is string[] {
return typeof arr === "object" && "length" in arr
}
is allows you to specify how the type of a variable is defined. That is, when the function returns true, the variable declared on the left will have the type on the right. That is when
if (isArrayString(arr)) {
// arr is string[] <-- The type that `is` specifies in the return . declaration
} else {
// arr is other type
}
