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Use hasOwnProperty with Typescript

Published by admin on 15. March 2022

Overview

Typescript does not support hasOwnProperty() function like javascript. To archive this we need to create an own helper function:

type Prop = string | number | symbol;

function hasOwnProperty<X extends {}, Y extends Prop>(obj: X, prop: Y): obj is X & Record<Y, unknown> {
  return obj.hasOwnProperty(prop)

Typescript Code

type Prop = string | number | symbol;
const  y = {name: "Helmut", id: 333}

function hasOwnProperty<X extends {}, Y extends Prop>(obj: X, prop: Y): obj is X & Record<Y, unknown> {
  return obj.hasOwnProperty(prop)
}

let propertyName = 'name';
if (hasOwnProperty(y, propertyName) ) {
  if (typeof y.name === 'string' && y.name) {
    console.log("--- Property " + propertyName +  " found - Content: "  + y.name);
  }
}
else {
    console.log("--- Property " + propertyName + " not found");
  } 

propertyName = 'id';
if (hasOwnProperty(y, propertyName) ) {
  if (typeof y.name === 'string' && y.id) {
    console.log("--- Property " + propertyName +  " found - Content: "  + y.id);
  }
}
else {
    console.log("--- Property " + propertyName + " not found");
  } 

propertyName = 'name2';
if (hasOwnProperty(y, propertyName) ) {
  if (typeof y.name === 'string' && y.name2) {
    console.log("--- Property " + propertyName +  " found - Content: "  + y.name2);
  }
}
else {
    console.log("--- Property " + propertyName + " not found");
  }

Output

[LOG]: "--- Property name found - Content: Helmut" 
[LOG]: "--- Property id found - Content: 333" 
[LOG]: "--- Property name2 not found"

Reference

Published inTypescript

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