Question

I am trying to have my form fields submit after the onchange event.

The Json value returned looks like this:

{ "data": [ { "name":"p_data1,KEY=1", "value":"2", "error":"no error" } ] } 

I am going to add an array to this sting to specify any other fields (such as ‘total’) which also need updating, like so:

{ "data": [ { "name":"p_data1,KEY=1", "value":"2", "error":"no error", "toUpdate": [ { "name":"p_total_data1" , "value":"999" } ] } ] } 

So I will only want to run the update total script when the toUpdate array exsists.
My issue is if I use an if statement like

if(typeof results.data[0].toUpdate[0].name == 'undefined'){}

or

if(null != results.data[0].toUpdate[0].name){}

or

if(results.data[0].toUpdate[0].name.length){}

All give the error “results.data[0].toUpdate[0].name is undefined”. How can I test whether it is defined?

Answer 1

You need to check to check for the existence of results.data[0].toUpdate before you attempt to access its properties:

if (results.data[0].toUpdate && results.data[0].toUpdate[0].name){
  // perform the update
}

If the first condition evaluates to false (or any “falsy” value), the && operator will short-circuit and won’t evaluate the second condition at all, preventing the error you’re seeing.