How to Iterate Through Mapped Type Record with Generic Value ?

In TypeScript, we can iterate through the mapped type record with the generic value by extracting the keys and the access its corresponding generic values. This mainly can be done using various approaches like loop, and builtin Object methods. In this article, we will explore three different approaches to iterate through mapped type records with generic values in TypeScript.

These are the following approaches:

Using for...in Loop

In this approach, we use for...in loop to iterate over the keys of a mapped type record with generic values. This basically, accesses each key by allowing the extraction of the corresponding generic value.

Syntax:

for (variable in object) {
  // code
}

Example: The below example uses for...in the loop to iterate through mapped type record with generic value in TypeScript.

Javascript

type obj1 = {
    topic: string;
    difficulty: number;
};
const gfgData: Record<string, obj1> = {
    algorithm: {
        topic: "Algorithms",
        difficulty: 3
    },
    dataStructure: {
        topic: "Data Structures",
        difficulty: 2
    },
    language: {
        topic: "Programming Languages",
        difficulty: 1
    },
};
for (const key in gfgData) {
    const data = gfgData[key];
    console.log(`${key}: ${data.topic}, 
    Difficulty: ${data.difficulty}`);
}

Output:

algorithm: Algorithms, Difficulty: 3
dataStructure: Data Structures, Difficulty: 2
language: Programming Languages, Difficulty: 1

Using Object.entries() method

In this approach, we use Objects.entries() method to iterate through the key-value pairs of the mapped type record with the generic values. the desstruuting of the entires mainly allows direct access to the key and its associated generic value.

Syntax:

Object.entries(obj) 

Example: The below example uses the Object.entries() method to iterate through mapped type record with generic values in TypeScript.

Javascript

type obj2 = {
    topic: string;
    difficulty: number;
};
const gfgData: Record<string, obj2> = {
    algorithm: {
        topic: "Algorithms",
        difficulty: 3
    },
    dataStructure: {
        topic: "Data Structures",
        difficulty: 2
    },
    language: {
        topic: "Programming Languages",
        difficulty: 1
    },
};
Object.entries(gfgData).forEach(([key, data]) => {
    console.log(`${key}: ${data.topic},
     Difficulty: ${data.difficulty}`);
});

Output:

algorithm: Algorithms, Difficulty: 3
dataStructure: Data Structures, Difficulty: 2
language: Programming Languages, Difficulty: 1

Using Object.keys() and forEach() methods

In this approach, we use the Object.keys() and forEach() method to iterate over the keys of mapped type record with the generic values. For each key, the associated generic value is retieved and printed.

Syntax:

Object.keys(myObject).forEach(key => console.log(`${key}: ${myObject[key]}`)); 

Example: The below example uses Object.keys() and forEach() methods to iterate through mapped type record with generic values in TypeScript.

Javascript

type obj3 = {
    topic: string;
    difficulty: number;
};
const gfgData: Record<string, obj3> = {
    algorithm: {
        topic: "Algorithms",
        difficulty: 3
    },
    dataStructure: {
        topic: "Data Structures",
        difficulty: 2
    },
    language: {
        topic: "Programming Languages",
        difficulty: 1
    },
};
Object.keys(gfgData).forEach((key) => {
    const data = gfgData[key];
    console.log(`${key}: ${data.topic},
     Difficulty: ${data.difficulty}`);
});

Output:

algorithm: Algorithms, Difficulty: 3
dataStructure: Data Structures, Difficulty: 2
language: Programming Languages, Difficulty: 1

Using Object.getOwnPropertyNames()

In this approach, we leverage the Object.getOwnPropertyNames() method to obtain an array of all property names of the mapped type record with generic values. We then iterate through these property names to access the corresponding generic values, enabling flexible handling of the record's contents.

Syntax:

Object.getOwnPropertyNames(obj)

Example:

JavaScript

type Topic = {
    name: string;
    difficulty: number;
};

const topics: Record<string, Topic> = {
    algorithm: {
        name: "Algorithms",
        difficulty: 3
    },
    dataStructure: {
        name: "Data Structures",
        difficulty: 2
    },
    language: {
        name: "Programming Languages",
        difficulty: 1
    },
};

Object.getOwnPropertyNames(topics).forEach((key: keyof typeof topics) => {
    const data = topics[key];
    console.log(`${key}: ${data.name}, Difficulty: ${data.difficulty}`);
});

Output:

"algorithm: Algorithms, Difficulty: 3" 
"dataStructure: Data Structures, Difficulty: 2" 
"language: Programming Languages, Difficulty: 1"