# Conditions

> Source: https://learn-typescript.org/conditions/
> Part of Learn TypeScript, free to read.

### The `if` statement

The `if` statement allows us to check if an expression is equal to `true` or `false`, and execute different code according to the result.

For example, if we want ask the user whether his name is “John”, we can use the `confirm` function.

```typescript
if (confirm("Are you John Smith?"))
{
    console.log("Hello John, how are you?");
} else {
    console.log("Then what is your name?");
}
```

It is also possible to omit the `else` keyword if we only want to execute a block of code only if a certain expression is true.

To evaluate whether two variables are equal, the `==` operator is used. There is also another equality operator in JavaScript, `===`, which does a strict comparison. This means that it will be true only if the two things you are comparing are the same type as well as same content.

```typescript
console.log("1" == 1); // true
console.log("1" === 1); // false
```

For example:

```typescript
let myNumber = 42;
if (myNumber == 42)
{
    console.log("The number is correct.");
}
```

Inequality operators can also be used to evaluate expressions. For example:

```typescript
let foo = 1;
let bar = 2;

if (foo < bar)
{
    console.log("foo is smaller than bar.");
}
```

Two or more expressions can be evaluated together using logical operators to check if two expressions evaluate to `true` together, or at least one of them. To check if two expressions both evaluate to `true`, use the AND operator `&&`. To check if at least one of the expressions evaluate to `true`, use the OR operator `||`.

```typescript
let foo = 1;
let bar = 2;
let moo = 3;

if (foo < bar && moo > bar)
{
    console.log("foo is smaller than bar AND moo is larger than bar.");
}

if (foo < bar || moo > bar)
{
    console.log("foo is smaller than bar OR moo is larger than bar.");
}
```

The NOT operator `!` can also be used likewise:

```typescript
let notTrue = false;
if (!notTrue)
{
    console.log("not not true is true!");
}
```

### The `switch` statement

The `switch` statement is similar to the `switch` statement from the C programming language, but also supports strings. The `switch` statement is used to select between more than two different options, and to run the same code for more than one option. For example:

```typescript
let rank = "Commander";
switch(rank)
{
    case "Private":
    case "Sergeant":
        console.log("You are not authorized.");
        break;
    case "Commander":
        console.log("Hello commander! what can I do for you today?");
        break;
    case "Captain":
        console.log("Hello captain! I will do anything you wish.");
        break;
    default:
        console.log("I don't know what your rank is.");
        break;
}
```

In this example, “Private” an “Sergeant” both trigger the first sentence, “Commander” triggers the second sentence and “Captain” triggers the third. If an unknown rank was evaulated, the `default` keyword defines the action for this case (optional). We must use the `break` statement between every code block to avoid the `switch` from executing the next code block.

Using the `switch` statement in general is not recommended, because forgetting the `break` keyword causes very confusing results.