Verify if an entity (either an object or a class) possesses a specific attribute

Question

Verify if an entity (either an object or a class) possesses a specific attribute

Imagine having a class like this:

module MyModule {
    export class MyClass {
       x:number;
       y:number;
    }
}

Now, let's say we have a string called "x". How can we determine if MyClass has the property "x"?

If an instance of MyClass is created and we use the following code:

myClassInstance.hasOwnProperty("x");

It will return false unless "x" has a default value assigned. However, we don't want to set default values for each property. It would be ideal if we could accomplish this without actually creating an instance of MyClass.

typescript

Answer 1

Answer №1

When TypeScript is translated into JavaScript for execution, the type information included in the TypeScript code is no longer accessible. Therefore, checking types at runtime in TypeScript is not possible.

To perform type checks during compile-time, one can utilize interfaces as demonstrated in the example below:

interface IHasY
{
    y:any;
}

class MyClassC {
    x:number;
    z:number;
}

class MyClassD {
    z:number;
}

function Verify(param: IHasY)
{
    // Perform an action with param.y 
}

var objC = new MyClassC();
var objD = new MyClassD();

Verify(objC);
Verify(objD);

The line Verify(objD); would trigger a compilation error because the TypeScript compiler recognizes that objD belongs to the MyClassD class, which does not contain a property named

y</code as mandated by the <code>IHasY

interface.

Answer 2

When TypeScript is translated into JavaScript for execution, the type information included in the TypeScript code is no longer accessible. Therefore, checking types at runtime in TypeScript is not possible.

To perform type checks during compile-time, one can utilize interfaces as demonstrated in the example below:

interface IHasY
{
    y:any;
}

class MyClassC {
    x:number;
    z:number;
}

class MyClassD {
    z:number;
}

function Verify(param: IHasY)
{
    // Perform an action with param.y 
}

var objC = new MyClassC();
var objD = new MyClassD();

Verify(objC);
Verify(objD);

The line Verify(objD); would trigger a compilation error because the TypeScript compiler recognizes that objD belongs to the MyClassD class, which does not contain a property named

y</code as mandated by the <code>IHasY

interface.

Answer 3

Answer №2

Exciting news! I have just unveiled an upgraded version of the TypeScript compiler that enables you to compile a comprehensive list of all members within a class or interface. This new feature opens up a world of possibilities for developers, allowing them to easily access and analyze data structures.

export class Person {
    name: string;
    surname: string;
    age: number;
    country: string;
}

function printMembers(clazz: Class) {
    let fields = clazz.members.filter(m => m.type.kind !== 'function'); //exclude methods.
    for(let field of fields) {
        let typeName = field.type.kind;
        if(typeName === 'class' || typeName === 'interface') {
            typeName = (<Class | Interface>field.type).name;
        }
        console.log(`Field ${field.name} of ${clazz.name} has type: ${typeName}`);
    }
}

//then, somewhere in your code:
let p = new Person();
printMembers(p.constructor.getClass());

This capability produces the following output:

$ node main.js
Field name of Person has type: string
Field surname of Person has type: string
Field age of Person has type: number
Field country of Person has type: string

To dive deeper into this groundbreaking feature, visit this link

Answer 4

Exciting news! I have just unveiled an upgraded version of the TypeScript compiler that enables you to compile a comprehensive list of all members within a class or interface. This new feature opens up a world of possibilities for developers, allowing them to easily access and analyze data structures.

export class Person {
    name: string;
    surname: string;
    age: number;
    country: string;
}

function printMembers(clazz: Class) {
    let fields = clazz.members.filter(m => m.type.kind !== 'function'); //exclude methods.
    for(let field of fields) {
        let typeName = field.type.kind;
        if(typeName === 'class' || typeName === 'interface') {
            typeName = (<Class | Interface>field.type).name;
        }
        console.log(`Field ${field.name} of ${clazz.name} has type: ${typeName}`);
    }
}

//then, somewhere in your code:
let p = new Person();
printMembers(p.constructor.getClass());

This capability produces the following output:

$ node main.js
Field name of Person has type: string
Field surname of Person has type: string
Field age of Person has type: number
Field country of Person has type: string

To dive deeper into this groundbreaking feature, visit this link

Verify if an entity (either an object or a class) possesses a specific attribute

Answer №1

Answer №2

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