What is Type Inference in TypeScript

TypeScript is a typed language. However, it is not mandatory to specify the type of a variable. TypeScript infers types of variables when there is no explicit information available in the form of type annotations

Types are inferred when:

• Variables are initialized
• Default values are set for parameters
• Function return types are determined

var a = "Typescript";
var b = 123;
a = b; // Compiler Error: Type 'number' is not assignable to type 'string'

function sum(a: number, b: number ){ 
	return a + b; 
}
var total: number = sum(10,20); // OK
var str: string = sum(10,20); // Compiler Error 

When Typescript can not infer the type the any type will be used

const canNotInfer = JSON.parse('{}');
// canNotInfer will have type: any