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Web Technologies - TypeScript

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Lesson Description


Lession - #1453 TypeScript Key Off


keyof is a keyword in TypeScript which is used to extract the key type from an object type.

keyof with explicit keys
When used on an object type with explicit keys, keyof creates a union type with those keys.

illustration

 interface Person{ 
 name string; 
 age number; 
 


keyof Person here creates a union type of" name" and" age", other strings won't be allowed


 function printPersonProperty( person Person, property keyof Person>
{ console.log( Printing person property${ property}"${ person( property>
}">
; let person = { name" Max", age 27 ; printPersonProperty( person," name">
;// Printing person property name" Max"


keyof with index signatures
keyof can also be used with index signatures to extract the index type.


 type StringMap = {( key string>
unknown}; / keyof StringMap resolves to string here function createStringPair( property keyof StringMap, value string>
StringMap{ return{( property>
value};


Online compiler