Is key-value pair available in Typescript?

Yes. Called an index signature:

interface Foo {
   [key: string]: number;
}


let foo:Foo = {};
foo['hello'] = 123;
foo = {
  'leet': 1337
};
console.log(foo['leet']); // 1337

Here keys are string and values are number.

More

You can use an es6 Map for proper dictionaries, polyfilled by core-js.

The simplest way would be something like:

var indexedArray: {[key: string]: number}

Usage:

var indexedArray: {[key: string]: number} = {
    foo: 2118,
    bar: 2118
}

indexedArray['foo'] = 2118;
indexedArray.foo= 2118;

let foo = indexedArray['myKey'];
let bar = indexedArray.myKey;

You can also consider using Record, like this:

const someArray: Record<string, string>[] = [
    {'first': 'one'},
    {'second': 'two'}
];

Or write something like this:

const someArray: {key: string, value: string}[] = [
    {key: 'first', value: 'one'},
    {key: 'second', value: 'two'}
];

Is key-value pair available in Typescript?

If you think of a C# KeyValuePair<string, string>: No, but you can easily define one yourself:

interface KeyValuePair {
    key: string;
    value: string;
}

Usage:

let foo: KeyValuePair = { key: "k", value: "val" };

Another simple way is to use a tuple:

// Declare a tuple type
let x: [string, number];
// Initialize it
x = ["hello", 10];
// Access elements
console.log("First: " + x["0"] + " Second: " + x["1"]);

Output:

First: hello Second: 10

Not for the questioner, but for all others, which are interested: See: How to define Typescript Map of key value pair. where key is a number and value is an array of objects

The solution is therefore:

let yourVar: Map<YourKeyType, YourValueType>;
// now you can use it:
yourVar = new Map<YourKeyType, YourValueType>();
yourVar[YourKeyType] = <YourValueType> yourValue;

Cheers!

A concise way is to use a tuple as key-value pair:

const keyVal: [string, string] =  ["key", "value"] // explicit type
const keyVal2 = ["key", "value"] as const // inferred type with const assertion
const [key, val] = ["key", "val"] // usage with array destructuring

You can create a generic KeyValuePair type for reusability:

type KeyValuePair<K extends PropertyKey, V = unknown> = [K, V]
const kv: KeyValuePair<string, string> = ["key", "value"]

TS 4.0

provides labeled tuple elements for better documentation and tooling support:

type KeyValuePairNamed = [key: string, value: string] // "key" and "value" labels

Compatibility

[key, value] tuples also ensure compatibility to JS built-in objects:

• Object, esp. Object.entries, Object.fromEntries
• Map, esp. Map.prototype.entries and new Map() constructor
• Set, esp. Set.prototype.entries

Playground

an example of a key value pair is:

[key: string]: string

you can put anything as the value, of course

One can also simple use Record

type Foo = Record<string, number>

Further usage in the docs

class Pair<T1, T2> {
    private key: T1;
    private value: T2;

    constructor(key: T1, value: T2) {
        this.key = key;
        this.value = value;
    }

    getKey() {
        return this.key;
    }

    getValue() {
        return this.value;
    }
}
const myPair = new Pair<string, number>('test', 123);
console.log(myPair.getKey(), myPair.getValue());

KeyValue interface exists in angular library that uses typescript. So you have this generic interface to use if your project is angular. Or you can use its declaration to get a nice generic KeyValue interface if you are not using TS in angular.

export declare interface KeyValue<K, V> {
    key: K;
    value: V;
}

TypeScript has Map. You can use like:

public myMap = new Map<K,V>([
[k1, v1],
[k2, v2]
]);

myMap.get(key); // returns value
myMap.set(key, value); // import a new data
myMap.has(key); // check data

const YAHOO = 'YAHOO';
const GOOGLE = 'GOOGLE';
const google = 'google';
const yahoo = 'yahoo';

type DomainKeyType = typeof GMAIL | typeof GOOGLE;
type DomainValueType = typeof google | typeof yahoo;

type DomainType = Record<DomainKeyType , DomainValueType>

const domain: DomainType = {
  YAHOO: yahoo,
  GOOGLE: google,
}

If you are trying to use below example

Example: { value1: "value1" }

And add conditionalData dynamically based on some condition, Try

let dataToWrite: any = {value1: "value1"};

if(conditionalData)
   dataToWrite["conditionalData"] = conditionalData