Recap: Fine-Tuning Types

Part of the Introduction To TypeScript section of Coddy's JavaScript journey — lesson 73 of 73.

Challenge

Easy

Create a configuration management system that processes dynamic settings using index signatures, type guards, and type assertions.

Create an interface named AppConfig that uses an index signature to map string keys to values of type string | number | boolean.

Create a function named validateConfigValue that:

Takes two parameters: config of type AppConfig and key of type string
Returns "missing" if the key doesn't exist in the config
Uses type guards to check the actual type of the value
Returns "string" if the value is a string
Returns "number" if the value is a number
Returns "boolean" if the value is a boolean
Has an explicit return type of string

Create a function named getConfigAsString that:

Takes two parameters: config of type AppConfig and key of type string
Returns "undefined" if the key doesn't exist
Uses a type assertion to treat the value as string and returns it if the value exists
Has an explicit return type of string

Create a function named processConfig that:

Takes two parameters: config of type AppConfig and key of type string
Uses validateConfigValue to check the type
Returns the value converted to uppercase if it's a string
Returns the value multiplied by 10 if it's a number
Returns the opposite boolean value if it's a boolean
Returns null if the key is missing
Has an explicit return type of string | number | boolean | null

Create test data:

Create settings of type AppConfig with:
- "appName": "MyApp"
- "version": 2.1
- "debugMode": true
- "maxUsers": 100
- "theme": "dark"

Test your functions and print the following outputs:

Call validateConfigValue with settings and "appName"
Call validateConfigValue with settings and "version"
Call validateConfigValue with settings and "debugMode"
Call validateConfigValue with settings and "timeout"
Call getConfigAsString with settings and "theme"
Call getConfigAsString with settings and "missing"
Call processConfig with settings and "appName"
Call processConfig with settings and "maxUsers"
Call processConfig with settings and "debugMode"
Call processConfig with settings and "invalid"

Try it yourself

// TODO: Write your code here

// Create the AppConfig interface


// Create the validateConfigValue function


// Create the getConfigAsString function


// Create the processConfig function


// Create test data - settings object


// Test the functions and print results
console.log(validateConfigValue(settings, "appName"));
console.log(validateConfigValue(settings, "version"));
console.log(validateConfigValue(settings, "debugMode"));
console.log(validateConfigValue(settings, "timeout"));
console.log(getConfigAsString(settings, "theme"));
console.log(getConfigAsString(settings, "missing"));
console.log(processConfig(settings, "appName"));
console.log(processConfig(settings, "maxUsers"));
console.log(processConfig(settings, "debugMode"));
console.log(processConfig(settings, "invalid"));

Recap: Fine-Tuning Types

All lessons in Introduction To TypeScript