How to parse string | number in Typescript?-CodePudding

I need add 40 to a string | number type, and return a string | number. How is it possible in Typescript?

I thought parse it to number, then increase it and return it. But how can I parse a variable which is not sure is string, but it can be number? :)

tried this:

parseInt(x) - 44

but raised an

Argument of type 'string | number' is not assignable to parameter of type 'string'.
  Type 'number' is not assignable to type 'string'.ts(2345)

CodePudding user response：

instead of parseInt use Number something like

Number(x)

CodePudding user response：

To add another option, you could simply make sure that what's passed to parseInt is a string using a template string:

parseInt(`${x}`)

CodePudding user response：

By checking the type:

if (typeof x === "string") {
    x = Number(x); // Or `parseInt` or whatever
}
const result = x - 44;

After the if, TypeScript will know from flow analysis that x has been narrowed from string | number to number.

Playground example

For the parsing, see my answer here for your various options. parseInt stops at the first non-numeric character and returns whatever number it has at that point (rather than returning NaN), which may or may not be your desired behavior.