Question

I have the following JSON Object:

{
  "a1_1_on" : "on",
  "a1_1_thr" : "",
  "a1_2_on" : "on",
  "a1_2_thr" : "",
}

and I want using a for loop to check the fields for example:

for (var i=1; i<2; i++) {
    //alarm
    var al = 'ai_' + i + '_on';
    //alarm threshold
    var althr = 'ai_' + i + '_thr'

    //console.log(form_infos.al);

    if(form_infos.al == "on" && form_infos.althr == "") {
        alert("Alarm for Analog " + i + "is on and you did not specified a threshold. Please specify a threshold before submittiing");
        return false;
    }
}

But it shows undefined if I do console.log(form_infos.al). Any suggestions?

Answer 1

There are several errors in your code.

First of all, In JSON ‘:’ is used between key and value, so it has to be

{
  "a1_1_on": "on",
  "a1_1_thr": "",
  "a1_2_on": "on",
  "a1_2_thr": "",
}

by the way this is not JSON, but a simple Javascript Object. JSON would be the String representation of that Object.

Second, your string to index the elements has a typo, you have

 "a1..."

in your Object but you use

 var al = 'ai_' + i + '_on';

in your code (i instead of 1)

Third, al is not an subobject of form_infos, but a variable containing a string. To access a subobject with a string index use

form_infos[al]

instead of

form_infos.al

That’s it