I intend the user to input a number in a form field field but the value I get back is a string (even when the input is type="number"!). For example, I often run into this when reading a value from an input field. This could happen for a number of reasons. You're writing a TypeScript application and you hit an error like this: Argument of type 'string' is not assignable to parameter of type 'number'.(2345) 3 min read Photo by Gerrie van der Walt.IMHO duplicate type checks should not be encouraged. ![]() Adding runtime checks creates bigger bundles and slower code (even if only by a tiny margin).In my opinion, the type system should allow relaying on the behavior: The spec gives the function the signature parseInt ( string, radix ) but also states that the argument will be converted to string internally ( Let inputString be ? ToString(string).). ![]() :/ const asNumber3 = typeof maybeNumber = 'string' ? parseInt ( maybeNumber, 10 ) : maybeNumber // Or simply accept defeat and out out const asNumber4 = parseInt ( maybeNumber as string, 10 ) Use the parseInt Built-In Function to Convert From String to Integer in TypeScript The parseInt function is used for conversion from string to integer, and the parseFloat function is used to convert from string to floating-point data type. If you really want to, add a type assertion, because this is a very dangerous process. This is not a process you should put arbitrary data through. But we are still duplicating a type check that already exits in the runtime. parseInt(3e20) is 3e20 but parseInt(3e21) is 3. If the value begins with '0x', JavaScript assumes radix 16. We can use the ‘+’ unary operator, Number (), parseInt () or parseFloat () function to convert string to number. If radix is omitted, JavaScript assumes radix 10. In typescript, there are numerous ways to convert a string to a number. A radix parameter specifies the number system to use: 2 binary, 8 octal, 10 decimal, 16 hexadecimal. Java, Kotlin, Typescript used that widely: Actually, double exclamation is not an operator. toString ( ), 10 ) // Or, better do a type check. Definition and Usage The parseInt method parses a value as a string and returns the first integer. As everybody knows, char notation just means the reverted logical state of the value. The Number.parseInt () El método Number.parseInt () analiza un argumento de cadena y devuelve un entero de la raíz o base especificada. The best way is to make use of the unary plus + operator or the Number global function. const asNumber2 = parseInt ( maybeNumber. The Number.parseInt () method parses a string argument and returns an integer of the specified radix or base. There are several ways you can convert Typescript String to Number. const asNumber1 = parseInt ( maybeNumber, 10 ) // So the solution would be: // Convert the number toString() and the string toString() so we can be sure that we never // pass numbers into the parseInt function. ![]() If radix is omitted, JavaScript assumes radix 10. Const maybeNumber: number | string = 1 // The issue: parseInt only accepts strings so this fails, // even though the runtime happily accepts any value. The Number.parseInt method parses a value as a string and returns the first integer.
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