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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