TypeError: Cannot read property 'url' of undefined, when actually testing for undefined

Question

In my react app I have state:

  const [functions, setfunctions] = useState([{}]);

A test for undefined:

if (typeof functions[functionCount].url !== "undefined") {
            imgSrc = functions[functionCount].url;
          } else {
            imgSrc = "";
          }

And a JSX element that displays the URL if there is one:

<img style={{ width: "100%" }} src={imgSrc}></img>

How am I still getting this error?

Because it's not .url that's undefined. It's the part before that that's undefined (functions[functionCount]) — Heretic Monkey
– Heretic Monkey, Commented Apr 27, 2020 at 19:17

larz · Accepted Answer · 2020-04-27 19:18:12Z

1

Check for the existence of functions[functionsCount] first -

if (functions[functionCount] && typeof functions[functionCount].url !== "undefined")

answered Apr 27, 2020 at 19:18

larz

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1 Comment

user1088793 Over a year ago

I can't tell you how many times over the last year whilst learning javascript I have banged my head against this issue. Finally I know.. :)

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