Javascript Notes: Variables

Intro

Like most languages, variables in Javascript are defined with the = operator.

There are 3 different keywords that can be used to define a variable.

• var - Depricated, should not be used for ES6+.
• let - Variable can be re-assigned. Value can be mutated.
• const - Variable cannot be re-assigned. Value can be mutated.

Define a Variable

// var syntax (considered depricated)
var name = "stuff";

// let syntax
// initialize variable without value assignment
// only available with "let" keyword
let name;

// initialize a variable and assign a value
let name = "stuff";

// re-assign a variable
let name = "things";

// const syntax
// initialize a constant and assign a value
// a value must be assigned when initialized
const name = "stuff";

// re-assigning a constant will result in a runtime error
const name = "things"; // => Uncaught SyntaxError: redeclaration of var name

Considerations

• camelCase is the convention used for multi-word variables.
• Variables can contain letters, numbers, underscores _ and a dollar sign $ .
• Variables cannot start with a number.
• let should be used when a variable may be overwritten such as in a for loop.
• const should be used when a variable should not be overwritten.