variable assignment

I have question on this Javascript code. i am a basic learner.

The books says that they need to assign the PurcahsePrice to 0 as they do not know what the purchase price is as they need the customer to key in the purchase price ( that is why the prompt command exist)

My question is , since the PurchasePrice = 0 is being replace by another value when the customer is keying in a new value to it ( at the prompt), Can i use values other than 0, i mean since the 0 value is gonna be replaced, i can use like 5, 34, or other values. Can i do that? if not, why not?

Thanks.

 

yeah you can definitely assign any number to that variable coz var PurchasePrice = 0; only means that you declare a variable and assign an initial value to it.

 

That means in order to declare a variable, you MUST assign an initial value to it first. I got to do that for every situation?

i cannot do this? : ( i have seen in example in books that they do that)

 

not it does not.

javascript is so very versatile... i have seen examples of really bad variable assignment, including in so called tutorials. things like pre-declaring the number of items you will have in an array (eg, var blah = new Array(30); )

so if you are going to use this within the scope of the same function/context why bother with the extra line and assignment?

var PurchasePrice = prompt('Please enter your purchase price'. '');

it only makes sense to declare variables if they need to be accessible throughout from functions / classes as global (or even local to the functions)

this would all be a valid way in declaring variables:

var foo, bar, moo = 43, messageUser = function(what) { alert("The answer to "+what+" is "+moo); }, items = [], myobject = {}, myobject2 = { 
    html: "bar",
    styles: {
        border: "1 px solid #000",
        padding: 2
    },
    className: "myWindow",
    className2: "myWindowFocused",
    events: {
        "onmouseover": function() {
            this.className = myobject2.className2;
        },
        "onmouseout": function() {
            this.className = myobject2.className;
        }
    }
}; // end variable declarations...

PHP: