Typescript: Deciphering how to interpret a string with a mix of characters and numbers

Is there a way in TypeScript to add 40 to a variable of type string | number, and return a result as a string | number?

My initial approach was to parse the variable to a number, then perform the addition, but how can I ensure that the variable is properly parsed if it could be either a string or a number?

I attempted the following:

parseInt(x) - 44

which resulted in the following error:

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

Answer №1

try replacing parseInt with Number like this:

Number(x)

Answer №2

If you want to include an additional choice, one way is to ensure that the input being passed to parseInt is in string format by utilizing a template literal:

parseInt(`${x}`)

Answer №3

After examining the data type:

if (typeof x === "string") {
    x = Number(x); // You could also utilize `parseInt` or another approach
}
const result = x - 44;

Once the if condition is met, TypeScript's analysis will determine that x has transformed from being a string | number to specifically a number.

Try it out here

To explore different techniques for parsing, you can refer to my detailed response here. When using parseInt, it will stop at the first non-numeric character and provide the numerical value up to that point (instead of returning NaN),

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