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I'd like to use string index of interface.
interface IDictionary { [index: string]: string; } var params: IDictionary; params = [{ "heart": "HP" }, { "mana": "MP" }]; console.log(params); I thought this might be like MAP such as a pair of key and value. I'm not sure this is correct approach.
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The "Type 'String' cannot be used as an index type" TypeScript error occurs when we use the String type instead of string (lowercase s ). To solve the error, make sure to use the string type with lowercase s in your TypeScript code.
The indexing type is itself a type, so we can use unions, keyof , or other types entirely: type I1 = Person ["age" | "name"]; type I1 = string | number. type I2 = Person [keyof Person ]; type I2 = string | number | boolean.
Interfaces and Inheritance An interface can be extended by other interfaces. In other words, an interface can inherit from other interface. Typescript allows an interface to inherit from multiple interfaces. Use the extends keyword to implement inheritance among interfaces.
Index signature syntax The syntax of an index signature is pretty simple and looks similar to the syntax of a property, but with one difference. Instead of the property name, you simply write the type of the key inside the square brackets: { [key: KeyType]: ValueType } .
Using the indexer limits what can be put or fetched for the object using the index syntax. E.g. foo is inferred to be of type string:
interface IDictionary { [index: string]: string; } var params = {} as IDictionary; params['heart'] = 'HP'; // okay var foo = params['heart']; // foo:string The following on the other hand is an error as it will not type check:
var bar:number = params['heart']; // ERROR params['heart'] = 234; // ERROR Complete demo:
interface IDictionary { [index: string]: string; } var params = {} as IDictionary; params['heart'] = 'HP'; // okay var foo = params['heart']; // foo:string var bar:number = params['heart']; // ERROR params['heart'] = 234; // ERROR If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
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