typescript: object is possible undefined, but i use if chained to check

Question

I have this code, but i get an error on this code underlined 'startups[i].logo' is possible undefined, why this error if I use if to check the values ?

  for (let i = 0; i < startups.length; i++) {
    let startup = startups[i];
    if (startups[i] && startups[i].logo && startups[i].logo.location) {
      aStartup.push({
        objectID: startups[i].id,
        logo: startups[i].logo.location,
      });
      batchCount ++;
    }

webstorm alert show the error, and when webstomr show error then the compile will give error too — DDave
– DDave, Commented Dec 20, 2018 at 22:42

Karol Majewski · Accepted Answer · 2018-12-21 01:42:27Z

1

Extract the nullable parts to local variables:

for (let i = 0; i < startups.length; i++) {
  const startup = startups[i];
  const logo = startup.logo;

  if (startup && logo && logo.location) {
    aStartup.push({
      objectID: startup.id,
      logo: logo.location
    });

    batchCount ++;
  }
}

This makes a difference because TypeScript knows all nullable scenarios have been eliminated within this block.

answered Dec 21, 2018 at 1:42

Karol Majewski

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