TYPESCRIPT

concat string typescript

var str1 = new String( "This is string one" ); 
var str2 = new String( "This is string two" ); 
var str3 = str1.concat(str2.toString());
console.log("str1 + str2 : "+str3)   
// str1 + str2 : This is string oneThis is string two

Concat Type TypeScript

//concat
type Concat<T extends Array<unknown>, U extends Array<unknown>> = [...T, ...U];
type Result = Concat<[1], [2]>; // expected to be [1, 2]