JavaScript is able to make decisions based on data. It can run code only when certain conditions are met.

To do this, we use conditional statements. A conditional statement checks a condition, and if it is true, executes some code.

Run these examples in the editor:

if (true) {
  console.log("code between the {} will run");
}

if (false) {
  console.log("this code will NOT run");
}

The first example logs a message to the console, showing us that the code inside the curly braces executed.

The second conditional statement does not execute because the if condition was false. Only values that resolve to true will execute. The second console.log will not execute, so it won't log anything to the console.

Using if with a Comparison Operator

Now try this example:

if (1 === 2) {
  console.log("does this code run?");
}

Nothing is logged to the console. Since the if condition wasn't met, the code between the curly braces didn't run.

Change the condition from 1 === 2 to 1 !== 2 and run it again.

This time we should see a message logged to the console. Since 1 !== 2 resolves to true, the code between the curly braces was executed.

Using if in a Function

This is an example of using an if statement in a function:

function isDivisibleBy5(number) {
  if (number % 5 === 0) {
    return true;
  }
  return false;
}
isDivisibleBy5(20);

Try running the function with different arguments to get different results.

Notice how the return statement ends the function immediately. When the function returns true, it stops executing. This behavior means a function will never return two values.