javascript initialize to undefined or null or ""

Question

Java script has many falsy values as I started learning. I have a program that gets values from a service and loads into an array like this:

function loadNames() {
    Global.names = // what should I use here? undefined, null, "", 0, {} or anything else
    var lnames = getLNames(); // this is doing some magic
        if ( lnames.length !== 0 ) {
            Global.names = new Array();
            for ( var i = 0; i < lnames.length; ++i)
                Global.names[i] = lnames[i];
    }
}

I want to know the right way of resetting Global.names. What is most appropriate here? In code I only want to check like if ( Global.names )

PS: I can't just take the return value into Global.names as the returned object is destroyed later. Hence, I need to do a deep copy

Thanks

Solution 1

Taken from JavaScript: the good parts :

"The if statement changes the flow of the program based on the value of the expression. The then block is executed if the expression is truthy. Here are the falsy values:

• false

• null

• undefined

• the empty string ''

• the number 0

• the number NaN "

So basically if you set your var to any of those values, you'll be able to do a if(var){...}

Solution 2

I think you should init GLobal.names = []; and than just check if Global.names.length != 0. If you want to reset it just make it an empty array again.

Solution 3

I think you'd be better off to initialize it as an array and test as

if ( Global.names.length )

Also, if you're just storing strings in the array you can simplify the function as

function loadNames() {
  Global.names = getLNames().concat();
}

Solution 4

You don't have to initialise it to anything. You can do:

if (!Global.names) Global.names = [];
// add members to Global.names

This can be one in one statement:

Global.names = Global.names : [];

If you want to reset it, then:

Global.names = [];

or

delete Global.names;

Solution 5

Setting it to null is good, as you know that the variable exists but hasn't been assigned a value. This way you can easily see the state - if it's undefined then you've forgotten to declare it, if it's null it has been declared but never assigned a value, and if it's an Array then you can test the length from there.

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Comments

[fearofawhackplanet]

This is not correct. If the value is null then it has been assigned a value (the null value). If you don't assign it anything, it will be undefined. The language never assigns to null implicitly.

[chrisfrancis27]

While that's a great example of initialising a variable with a ternary statement, I don't think it quite answers the OP's question, as he is explicitly trying to clear the value of Global.names, while your code will not change its value.

[chrisfrancis27]

Actually yeah, you're right - what I really meant was that it has been assigned a 'falsy' value which is unlikely to be confused later with a valid value such as [].

[fearofawhackplanet]

Yes I agree with your approach