Object Properties

• Properties should be an identifier, not a string or expression: object.property
• You can list all properties with:

function DisplayPropertyNames(o){
        var names ="";
        for (var name in o) {
                names += name + " ";
        }
        alert(names);
}

DisplayPropertyNames(document)

• You can check if a property exists with:

//If o has property named "x" then set it
if ("x" in o) {
        o.x = 1;
 }

//If "x" exists and is not undefined, set it
if (o.x !== undefined) {
        o.x = 1;
 }