Understand JavaScript statements (variables, operators, functions)

21 Programming for the web

Variables – Your Digital Storage Boxes

Variables are like digital storage boxes that hold data. Think of them as labeled jars where you can keep different kinds of items – numbers, words, or even whole lists. In JavaScript you can create a variable with let, const or var (the last one is older, so we’ll focus on let and const).

• let age = 15; – age can change later.
• const PI = 3.14159; – PI stays the same.
• Variable names can include letters, numbers, $ and _ but must start with a letter, $ or _.

You can update a variable: age = age + 1; – now age becomes 16. This is like moving a toy from one box to another and changing its label.

Operators – The Digital Toolbox

Operators are the tools that let you manipulate data. They can add, subtract, compare, or even combine strings. Below is a quick reference table.

Remember: Operator precedence decides the order of operations. Use parentheses () to group calculations, just like you’d group ingredients in a recipe.

Functions – Your Reusable Recipes

Functions are like recipes that you can reuse whenever you need them. They take inputs (called parameters), do something, and may give you a result (return value). A function looks like this:

function greet(name) {
    return 'Hello, ' + name + '!';
}

Calling the function: greet('Alice'); gives 'Hello, Alice!'. 🎉

1. Define the function with function keyword.
2. Give it a name that describes what it does.
3. List any parameters inside parentheses.
4. Write the code block inside curly braces {}.
5. Use return to send back a value.

You can also create anonymous functions (without a name) and assign them to variables:

const square = function(x) {
    return x * x;
};

Now square(4) returns 16. 🔢

Key points:

• Functions keep your code organized and reusable.
• They can be nested – a function inside another function.
• JavaScript functions are first-class citizens, meaning you can pass them around like any other value.