How can I determine the types of values in a string[] | object[] array to perform different operations based on the value type?
I attempted to check the type of the first item in the array, but TypeScript does not recognize it and still considers it as string[] | object[].
I also tried using every method to verify each value type, however TypeScript does not permit the use of every or filter functions with string[] | object[] arrays.
When your array is defined as string[] | object[], it's a good idea to create a type predicate to determine its actual type:
function isArrayString(a_arr: string[] | object[]): a_arr is string[] {
return !a_arr.some(a_item => typeof a_item !== 'string');
}
This is how you can implement it:
if(isArrayString(arr)){
console.log(arr); // string[]
}
While it's possible to check the type in a loop using for or forEach, since your array is either string[] OR object[], it may not be the most practical approach.
let strings: string[] = ['x', 'y', 'z'];
//verify the variable type
const isStringArray = Array.isArray(strings); // 👉️ true
console.log(isStringArray)
//check the data types in the array
if (Array.isArray(strings)) {
const allStrings =
strings.length > 0 &&
strings.every((item) => {
return typeof item === 'string';
});
console.log(allStrings); // 👉️ true
}
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