[typescript] How do I convert a string to enum in TypeScript?

Simplest approach

enum Color { Red, Green }

const c1 = Color["Red"]
const redStr = "Red" // important: use `const`, not mutable `let`
const c2 = Color[redStr]

This works both for numeric and string enums. No need to use a type assertion.

Unknown enum strings

const redStrWide: string = "Red" // wide, unspecific typed string
const c3 = Color[redStrWide as keyof typeof Color]

const isEnumName = <T>(str: string, _enum: T): str is Extract<keyof T, string> =>
    str in _enum
const enumFromName = <T>(name: string, _enum: T) => {
    if (!isEnumName(name, _enum)) throw Error() // here fail fast as an example
    return _enum[name]
}
const c4 = enumFromName(redStrWide, Color)

Convert string enum values

String enums don't have a reverse mapping (in contrast to numeric ones). We can create a lookup helper to convert an enum value string to an enum type:

enum ColorStr { Red = "red", Green = "green" }

const c5_by_name = ColorStr["Red"] // ? this works
const c5_by_value_error = ColorStr["red"] // ? , but this not

const enumFromValue = <T extends Record<string, string>>(val: string, _enum: T) => {
    const enumName = (Object.keys(_enum) as Array<keyof T>).find(k => _enum[k] === val)
    if (!enumName) throw Error() // here fail fast as an example
    return _enum[enumName]
}

const c5 = enumFromValue("red", ColorStr)

Playground sample