How to check if a variable exist in jquery

Question

I have two variables in a jquery code and if item.a not exist, it outputs a 'null' so i want to check if the variable exists. Here's the code:

.append( "<a>" + item.a + ", " + item.b + "</a>" )

If there is no "item.a" it results in

null, Blabla

I tried this if / else statement but it returns nothing

.append( "<a>" + (item.a) ? item.a : + ", " + item.b + "</a>" )

Any idea?

Use native JavaScript, see: stackoverflow.com/questions/2703102/typeof-undefined-vs-null for more details. — StuperUser
– StuperUser, Commented Jul 5, 2012 at 11:01
strictly speaking you do not need an existence check - if the value is null you need a falsey check. — Alnitak
– Alnitak, Commented Jul 5, 2012 at 11:07

James Allardice · Accepted Answer · 2012-07-05 11:00:26Z

5

Your attempt was close. Try this instead:

.append( "<a>" + (item.a ? item.a : "") + ", " + item.b + "</a>" )

Or, assuming you don't want the comma when you don't have item.a:

.append( "<a>" + (item.a ? item.a + ", " : "") + item.b + "</a>" )

answered Jul 5, 2012 at 11:00

James Allardice

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1 Comment

@Alnitak - Yeah, probably. I've added that in.

Adil · Accepted Answer · 2012-07-05 11:14:33Z

1

The condition operator you use

EDIT

.append( "<a>" + (item.a != null ? item.a + ", " : "") + item.b + "</a>" )

If variable is null

if(varName === null)
{
    alert("variable has null");
}

If variable does not exists

if(typeof varName === 'undefined')
{
    alert("variable not defined");
}

answered Jul 5, 2012 at 11:00

Adil

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The variable isn't undefined; it's null instead, so your code won't work.