how to check null in javaScript function?

Question

I want to check null and empty id in JavaScript function,but if syntax isn't work ?

var id = "<%=Request["Id"]%>";
 if (id !== "")
 if (id !== null)
{var id = "<%=new Guid(Request["ID"].ToString())%>";
 window.location = "/Controller/Action.aspx?Id=" + id; }

codelock · Accepted Answer · 2016-09-11 09:33:14Z

1

With javascript,

If you are trying to test for not-null (any value that is not explicitly NULL) this should work for you:

if( myVar !== null ) { 
    // your code
}

If you are only interested to test for not-empty (null value, zero number, empty string etc..) then try:

if( !myVar ) { 
    // your code
}

If you want to test for if a variable is defined at all (which I believe is what you are trying to achieve) then you can do it like:

if( typeof myVar !== 'undefined' ) { 
    // your code
}

Please let me know if it works for you.

answered Sep 11, 2016 at 9:33

codelock

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Comments

jedifans · Accepted Answer · 2016-09-11 08:58:12Z

0

Read into binary logic:

var id = "<%=Request["Id"]%>";
if (id !== "" && id != null)  {
    var id = "<%=new Guid(Request["ID"].ToString())%>";
    window.location = "/Controller/Action.aspx?Id=" + id;
}

Then again, var id = "<%=Request["Id"]%>"; will never be null, only empty string, so perhaps you can drop that check altogether.

answered Sep 11, 2016 at 8:58

jedifans

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6 Comments

Elham Over a year ago

if (id !== "" && id != null)

jedifans Over a year ago

Are you sure? It's valid JavaScript so perhaps it's ASP doing something?

Elham Over a year ago

I search about && syntax in java script and concluded that separated if syntax

jedifans Over a year ago

Try with a regular html page, separate ifs may work with the braces in the right places but binary logic is far easier to read.

Elham Over a year ago

I try it but if condition passed. how can i see value of id ? with alert syntax?

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