TypeScript - if else

An if statement can include one or more expressions which return boolean. If the boolean expression evaluates to true, a set of statements is then executed.

if (true) 
{
    console.log('This will always executed.');
}

if (false) {
    console.log('This will never executed.');
}    

The following example includes multiple boolean expressions in the if condition.

let x: number = 10, y = 20;

if (x < y) 
{
    console.log('x is less than y');
} 

In the above example, the if condition expression x < y is evaluated to true and so it executes the statement within the curly { } brackets.

if else Condition

An if else condition includes two blocks - if block and an else block. If the if condition evaluates to true, then the if block is executed. Otherwies, the else block is executed.

let let x: number = 10, y = 20;

if (x > y) 
{
    console.log('x is greater than y.');
} 
else
{
    console.log('x is less than or equal to y.'); //This will be executed
}

In the above example, the else block will be executed. Remember: else cannot include any condition and it must follow if or else if conditions.

else if

The else if statement can be used after the if statement.

let x: number = 10, y = 20;

if (x > y) 
{
    console.log('x is greater than y.');
} 
else if (x < y)
{
    console.log('x is less than y.'); //This will be executed
}
else if (x == y) 
{
    console.log('x is equal to y');
}

Ternary operator

A ternary operator is denoted by '?' and is used as a short cut for an if..else statement. It checks for a boolean condition and executes one of the two statements, depending on the result of the boolean condition.

Boolean expression? First statement : second statement

let x: number = 10, y = 20;

x > y? console.log('x is greater than y.'): console.log('x is less than or equal to y.')

x is less than or equal to y.

In the above example, condition x > y is turned out be to false, so the second statement will be executed.