Two Ways to Force Types in TypeScript
There are two ways to force types in TypeScript (also known as type casting or type conversion). Using the bracket syntax, or using the
as keyword. For example:
// Using bracket syntax const age = <string>user.age // Using the "as" keyword const age = user.age as number
In the above code example, we are transforming one type into another, for example, a number to a string, or a string to a number. In both cases, the end result will be the same, there are no differences.
One thing to keep in mind is to stick to one or the other for consistency. In case you don't know the type upfront, it is also a common practice to use the
any type to avoid type errors:
// Using bracket syntax const age = <any>user.age // Using the "as" keyword const age = user.age as any
Only use the
any type as the last resort, and if you are sure your application won't run into type errors.
Type Conversions in TypeScript
Number object to convert strings to numbers and vice versa.
// Converting a string to a number const age: number = Number(user.age) // Converting a number to a string const age: string = String(user.age) // Make sure you pass a valid numbe to Number const age: number = Number('invalid') // This will result in NaN
Note that in case you pass an invalid number to the
Number object, you will get
NaN as a result. You can also convert types into booleans using the
Boolean(1) // Returns true Boolean('0') // Returns true Boolean() // Returns true Boolean(null) // Returns false Boolean(undefined) // Returns false Boolean(0) // Returns false Boolean(NaN) // Returns false
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