Mastering TypeScript 3 - Third Edition

The let keyword

Variables in JavaScript are defined by using the var keyword. Unfortunately, the JavaScript runtime is very lenient on where these definitions occur, and will allow a variable to be used before it has been defined. If the JavaScript runtime comes across a variable that has not been previously defined, or given a value, then the value for this variable will be undefined. Consider the following code:

console.log(`anyValue = ${anyValue}`); 
var anyValue = 2; 
console.log(`anyValue = ${anyValue}`); 

Here, we start by logging the value of a variable named anyValue to the console. Note, however, that the anyValue variable is only defined on the second line of this code snippet. In other words, we can use a variable in JavaScript before ...