TypeScript 2.x By Example

Type inference

One of the main features of JavaScript is that it's a dynamically typed language. This means a type of a variable is determined at runtime and the compiler does not generate any errors if there is a type mismatch until it fails. We can have the same variable hold a string, a number, an array, or an object and JavaScript will not complain, but it can cause errors at runtime if not handled. JavaScript uses type inference to identify the type of data stored in a variable, based on which it operates on the variable. The following is an example where type inference fails between a number and a string.

In the following code, when num is assigned a value of 1, JavaScript infers it as a number and performs addition when we try to add ...