JavaScript Fundamentals: Scope Lab

Learning Goals

• Use const and let to fix the scope in JavaScript

Introduction

ES6 gives us new ways to declare variables that help us out with scoping. The var keyword defines a variable globally or locally to an entire function regardless of block scope. With const and let, declaring variables with var is generally discouraged. In this lab, you'll need to debug some issues related to function scope in JavaScript: variables might not be what we expect, certain variables might be unavailable, and in general the current code might be a little chaotic.

Use const and let to Fix the Scope in JavaScript

To review:

• A variable or function that is not declared inside a function or block is the global execution context.
• let variables are block-scoped, and allows you to declare variables that are limited in scope to the block, statement, or expression on which it is used
• const is also block-scoped restricts over-writing variables. It does not mean the value it holds is immutable, just that the variable identifier cannot be reassigned. const variables also cannot be declared a without assigning its (constant) value
• Variables declared with var are not block-scoped, and leaves room for error

In index.js, we've given you some starter code. As is, it does not run. Start by running the specs and reading the results. Debug and make some fixes in the code. Run the tests again and repeat. Using your knowledge of scope, access and change the variables until all tests pass. Make sure to focus on using const and let and avoid usage of var, or you may experience some unexpected issues.

Resources

• MDN: Scope
• MDN: const
• MDN: let