I am facing a problem while trying to convert a string to a number. I have an age property in my JsType which is of type number, but I’m mapping an array of JsonType, which has a property age of type number:
interface JsType{
name: string
age?: number
//... more fields
}
interface JsonType{
name: string
age?: string
//... more fields
}
const filterData: JsType[] = [{name: 'magnus'}, {name:'hikaru',age: "50"}].map((item: JsonType): JsType => {
//item.age is of type string, i want it to be of type number
let age: number | null = item.age ? Number(item.age):null
let obj = {...(age?{age}:{}) }
const doc = { ...item, ...obj }
return doc
//ts error
// Types of property 'age' are incompatible.
// Type 'string | number | undefined' is not assignable to type 'number | undefined'.
// Type 'string' is not assignable to type 'number'.
})
The compilation error happens when returning doc object:
Types of property 'age' are incompatible.
Type 'string | number | undefined' is not assignable to type 'number | undefined'.
Type 'string' is not assignable to type 'number'.
How can I convert the string without getting the compilation error?
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3
The solution is simple, you’re declaring a obj variable for no reason, just use this approach instead:
interface JsType{
name: string
age?: number
//... more fields
}
interface JsonType{
name: string
age?: string
//... more fields
}
const filterData: JsType[] = [{name: 'magnus'}, {name:'hikaru',age: "50.5"}].map((item: JsonType): JsType => {
let age = item.age ? Number(item.age) : undefined;
const doc = { ...item, age }
return doc
})
this should work
Your Javascript is wrong too if you want to be strict. What you try is to add age only when it’s truthy, but you leave it in ...item in case it for example an empty string.
So I would suggest the following (removing age by destructuring):
interface JsType{
name: string
age?: number
//... more fields
}
interface JsonType{
name: string
age?: string
//... more fields
}
const filterData: JsType[] = [{name: 'magnus'}, {name:'hikaru',age: "50"}].map((item: JsonType): JsType => {
let age: string | undefined, out: JsType;
({age, ...out} = item);
if(age) out.age = Number(age);
return out;
})