如何在不使程序崩溃的情况下检查不存在的变量的值？

Question

I have a JSON output from an HTTP get. I am then using JSON.parse from nodejs.

The output is basically like this:

items: [
    snippet: {
        foo: "bar",
        bar: "foo
    }
    snippet: {
        foo: "bar",
        bar: "foo
    }
    snippet: {
        foo: "bar",
        bar: "foo
    }
]

My code is then as such:

foo1 = items[0].snippet.foo
bar1 = items[0].snippet.bar

this variable declaration all works fine, until I get to the variables that might not exist sometimes.

foo4 = items[4].snippet.foo

Of course, this right here does not exist. I thought that I would be able to simply do an if(foo4 == 'Null') then set foo4 = 'not existing' so it does not crash my program later. However, the program crashes when DECLARING this variable itself... how can I prevent this from happening?

Answer 1

in ES2020 there is cool feature called optional chaining and nullish coalescing , so you can try to combine them:

foo4 = items[4]?.snippet?.foo ?? 'not existing'

So if items[4] is null or undefined part items[4]?.snippet?.foo will set undefined to foo4 and then operator ?? will add default value to variable foo 4