Variables with let and const

A variable is a named box that holds a value.

TypeScript uses the same let and const as JavaScript.

Each name also has a type name tag.

Start with const. Use let only when the value must change.

const for names that stay put

const stops you from giving that name a new value.

The box keeps the same toy.

For objects and arrays, the insides can still change.

An object is a bag of named values.

An array is a list.

let when the value changes

Use let for counters, flags, and anything you reassign.

A flag is a yes or no switch.

TypeScript still locks the type after the first value.

Or after you write a type yourself.

Widen carefully with types

Widen means open the name tag to allow more values.

Without a type, a string may be treated as that exact word.

Writing string opens up what you can assign later.

A union opens it to a few choices. We cover that soon.

Skip var

var is older.

It can surprise you with how it scopes.

Scope means where a name can be seen.

TypeScript still allows var so old code works.

Stick to let and const in new code.

Name things clearly

Pick names a friend can read.

Use camelCase for variables.

camelCase means firstWordThenNextWords.

Default to const. Use let when you need to reassign.