[JS] 05. Conditional_Code

05_Conditional_Code.html

<script>
//Flow control
var foo = true;
var bar = false;

if ( bar ) {
    // This code will never run.
    console.log( "hello!" );
}

if ( bar ) { 
    // This code won't run. 
} else { 
    if ( foo ) {
        // This code will run.
    } else {
        // This code would run if foo and bar were both false.
    } 
}



// [Truthy and Falsy Things]
// Values that evaluate to false:
false;
""; // An empty string.
NaN; // JavaScript's "not-a-number" variable.
null;
undefined; // Be careful -- undefined can be redefined!
0; // The number zero.

//Everything else evaluates to true, some examples:
"0";
"any string";
[]; // An empty array.
{}; // An empty object.
1; // Any non-zero number.



// [Conditional Variable Assignment with the Ternary Operator]
//Set foo to 1 if bar is true; otherwise, set foo to 0:
var foo = bar ? 1 : 0;



// [Switch Statements]
switch ( bar ) { 
    case "bar":
        alert( "the value was bar -- yay!" );
        break;

    case "baz":
        alert( "boo baz :(" );
        break;

    default:
        alert( "everything else is just ok" );

}

//Switch statements have somewhat fallen out of favor in JavaScript, 
//because often the same behavior can be accomplished by creating an object 
//that has more potential for reuse or testing. For example:
var stuffToDo = {   
     "bar": function() {
         alert( "the value was bar -- yay!" );
     },
  
     "baz": function() {
         alert( "boo baz :(" );
     },
  
     "default": function() {
         alert( "everything else is just ok" );
     }
  
 };
  
 // Check if the property exists in the object.
 if ( stuffToDo[ "foo" ] ) {
     // This code won't run.
     stuffToDo[ "foo" ]();  
 } else {
     // This code will run.
     stuffToDo[ "default" ]();  
 }
</script>