var, let, and const

Variables declared with var:

• Are function or global scoped
• Can be used before they're declared
• Generally not recommended in modern JavaScript files

Variables declared with let:

• Are block scoped
• Can’t be used before declared
• Can have their value reassigned
• Recommended more than var, especially if you need to reassign the value

Variables declared with const:

• Are block scoped
• Can’t be used before declared
• Can’t have their value reassigned
• Recommended first choice for declaring variables

These are my personal opinions. There's no "right" or "wrong" way to declare the variables, but it's important to choose a method and then stick with it.

For more information on this topic, check out this blog post.