JavaScript proper way to handle null in JSON object

Question

Here is the code :

for (i = 0; i < data.RecruitingGroups.length; i++) {
        data.RecruitingGroups[i].id = i;

        if (data.RecruitingGroups[i].Rule.Rules != null) {
            for (j = 0; j < data.RecruitingGroups[i].Rule.Rules.length; i++) {
                data.RecruitingGroups[i].Rule.Rules[j].id = j;
            }    
        } 
    }

Problem is that sometimes RecruitingGroups[].Rule is null. So I tried to verify it was not null before continuing and running the next for loop, but it still throws the error:

Uncaught TypeError: Cannot read property 'Rules' of null

How can i bypass this error.

T McKeown · Accepted Answer · 2014-04-09 17:45:58Z

1

your second loop needs to increment j++ not i++. =)

answered Apr 9, 2014 at 17:45

T McKeown

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1 Comment

T McKeown Over a year ago

i like this allen dude!

user229044 · Accepted Answer · 2014-04-09 17:36:41Z

1

You're testing if Rule.Rules is null. That's not the problem; Rule itself is null, as evidenced by the error message. You need to test both Rule and Rule.Rules if either can be null.

Try

if (data.RecruitingGroups[i].Rule && data.RecruitingGroups[i].Rule.Rules) {

answered Apr 9, 2014 at 17:36

user229044♦

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3 Comments

allencoded Over a year ago

same error Uncaught TypeError: Cannot read property 'Rules' of null

user229044 Over a year ago

Then you're accessing Rule.Rules somewhere else without first checking if Rule is not null. The code I've posted cannot produce that error; it's impossible for my if statement to attempt to access Rule.Rules if Rule is null.

allencoded Over a year ago

Found problem i++ was in second for loop. should be j++

T McKeown · Accepted Answer · 2014-04-09 17:36:32Z

-1

 if (data.RecruitingGroups[i].Rule && data.RecruitingGroups[i].Rule.Rules) {
        for (j = 0; j < data.RecruitingGroups[i].Rule.Rules.length; i++) {
            data.RecruitingGroups[i].Rule.Rules[j].id = j;
        }    
    }

answered Apr 9, 2014 at 17:36

T McKeown

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6 Comments

Ibu Over a year ago

because Rule is the one that is null, not Rules

user229044 Over a year ago

Your doing the same thing the original code is doing, and you're going to be producing the exact same error.

T McKeown Over a year ago

i read Uncaught TypeError: Cannot read property 'Rules' of null meaning that Rules was the issue, i will correct.

user229044 Over a year ago

Now your answer contains an obvious syntax error, and it also happens to be identical to my answer, except without any explanation of what was wrong or what has been fixed.

allencoded Over a year ago

problem was in the second for loop. j++ was needed not i++

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