Dealing with javascript undefined objects/arrays within an if statement

Question

I am catching errors from an Ajax response. The kind of error that comes back depends on where it was thrown and I need to look out for certain ones.

I know the error variable always exists but past this I have to check the existence for each level, otherwise risk getting a TypeError: Cannot read property '0' of undefined error.

I am currently doing:

if (error.response && error.response.data && error.response.data.errors 
&& error.response.data.errors[0].title === 'no_space') {
   //do something
}

But there must be a better way?

I think what you are looking for could be coming soon - optional chaining - dev.to/sammyisa/… — Paul Fitzgerald
– Paul Fitzgerald, Commented Nov 1, 2018 at 11:10
“But there must be a better way?” - why is this so convoluted in the first place? If you are in charge of the script that generates this structure in the first place, I’d maybe start by simplifying things there. error.response.data.errors seems rather redundant to begin with. — misorude
– misorude, Commented Nov 1, 2018 at 12:39

Nina Scholz · Accepted Answer · 2018-11-01 11:11:43Z

1

You could reduce the keys and take the final value for a check.

var keys = ['response', 'data', 'errors', 0, 'title'];
if (keys.reduce((o, k) => (o || {})[k], error) === 'no_space') {
    // ...
}

answered Nov 1, 2018 at 11:11

Nina Scholz

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2 Comments

Adam Lambert Over a year ago

I assume for this to work I would always need to know all the keys to get to the final value?

Nina Scholz Over a year ago

right, you need to know all keys in advance. what use case do you have?

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