1.8_Conditionalbranching.html

<!DOCTYPE html>
<html>
    <head>
        <script>
            // Conditional branching: if,?
            //if statement: used to check if a condition is true or not. If true a block of code is executed
            let year=prompt('In which year ECMAScript-2015 specification published?');
            if (year == 2015) 
            {
                alert('You are right!');
            }
            /*Boolean coverstion: by default, the condition results as a boolean value i.e., true/false.
            Recall type conversions:
            Falsy values: 0,"",null, undefined,NaN become false
            Truthy values: rest all become true
            */
           if(0)
           {
            // this code will never execute as condition will always be false
            alert(false);
           } 
           if(1)
           {
            // this code will always execute as condition will always be true
            alert(true);
           } 
           //if-else statement: similar to if, a block will be executed if true, another will be executed when false 
           year=prompt('In which year ECMAScript-2015 specification published?');
            if (year == 2015) 
            {
                alert('You are right!');
            }
            else
            {
                alert('You are wrong!');
            }
            //if-else if statement: used to check several conditions
            year=prompt('In which year ECMAScript-2015 specification published?');
            if (year > 2015) 
            {
                alert('Too late!');
            }
            else if(year < 2015)
            {
                alert('Too early!');
            }
            else
            {
                alert('Correct!');
            }
            /* Conditional operator '?': works similar to if else, is used to make the code shorter
            let result = condition ? value 1 : value 2
            It works such that if the condition is true then value 1 will be executed, otherwise value 2 will be executed
            */
            let accessAllowed;
            let age = prompt('How old are you?', '');
            alert(accessAllowed = (age > 18) ?  true : false);
            // Here, ? can be omitted as expression comparision by default returns a boolean
            alert(accessAllowed = (age > 18));
            /* Multiple '?': works like nested if/if else if. When we want to check multiple conditions
            */
           age=prompt('age?',18);
            
           let message = (age < 3) ? 'Hi, baby!' :
                        (age < 18) ? 'Hello!' :
                        (age < 100) ? 'Greetings' :
                        'What an unusual age!';
            alert(message);
        </script>
    </head>
</html>