TypeScript Union - Syntax & Examples - Tutorial Kart

TypeScript Union ¨C Syntax & Examples

TypeScript Union

A TypeScript Union variable can hold a value that belongs to one of the many declared datatypes.

Syntax of TypeScript Union

To specify the different datatypes that a union variable can hold, use the following syntax:

var varname: datatype1|datatype2|datatype3

var is the keyword

varname is the name of the union variable

datatype1, datatype2, . . datatypes that the variable can hold should be separated by vertical bar

Example

Following is an example of TypeScript Union, where a variable can hold data of either number or string.

example.ts

var ns : number|string

ns = 25

console.log("type of ns is : "+(typeof ns))

console.log("value of ns : "+ns)

ns = "Twenty Five"

console.log("\ntype of ns is : "+(typeof ns))

console.log("value of ns : "+ns)

On traspiling the code, following JavaScript is generated.

example.js

var ns;

ns = 25;

console.log("type of ns is :

console.log("value of ns : "

ns = "Twenty Five";

console.log("\ntype of ns is

console.log("value of ns : "

" + (typeof ns));

+ ns);

: " + (typeof ns));

+ ns);

Try executing the JavaScript online ¨C Try JavaScript Online.

Output

type of ns is : number

value of ns : 25

type of ns is : string

value of ns : Twenty Five

Union Type with Arrays

Even TypeScript Array can be declared as union type variable, i.e., the array variable can hold array of

elements that belong to any a given set of datatypes.

Example

In the following example, variable b is declared as a union type variable that can hold either a number or

number array.

example.ts

var a : number

var b : number|number[]

a = 10

b = 5

var c = a + b

console.log("sum of a and b : "+c)

b = [4, 8, 9, 1, 5, 6]

var c = a

b.forEach(i => {

c = c+i

})

console.log("sum of a and b : "+c)

When traspiled to JavaScript, following .js file is generated.

example.js

var a;

var b;

a = 10;

b = 5;

var c = a + b;

console.log("sum of a and b : " + c);

b = [4, 8, 9, 1, 5, 6];

var c = a;

b.forEach(function (i) {

c = c + i;

});

console.log("sum of a and b : " + c);

Execute the .js code using Try Online JavaScript.

Output

sum of a and b : 15

sum of a and b : 43

Conclusion

In this TypeScript Tutorial ¨C TypeScript Union, we have learnt how to declare a variable as union type. We

also looked into the declaration of array variables as union type.

TypeScript

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TypeScript Tutorial

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TypeScript Variables

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TypeScript if

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TypeScript if-else

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TypeScript Switch

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TypeScript For Loop

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TypeScript While Loop

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TypeScript Do-While Loop

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TypeScript Arrays

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TypeScript Tuples

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TypeScript Unions

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TypeScript Functions

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TypeScript Anonymous Functions

TypeScript Object Oriented Concepts

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TypeScript Class

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TypeScript Inheritance

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TypeScript Method Overriding

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TypeScript Interface

TypeScript String Operations

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TypeScript String Length

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TypeScript String Split

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