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javascriptfor-of-loop

How to write a more concise for-of loop

I have a for-of loop which goes like this:

for(const val of someArray[0].properties) {
 // some processing;
}

Now for some reason if someArray[0].properties is undefined, the loop breaks, saying:

Cannot read property 'Symbol(Symbol.iterator)' of undefined

If I try to use the !! shorthand for boolean operators:

for (const val of !!someArray[0].properties && someArray[0].properties) {
}

it fails again.

The only solution I could come up with was:

if(someArray[0].properties){ // this will check for that undefined issue
    for(const val of someArray[0].properties) {
     // some processing;
    }
}

Is there a more concise solution than this?

Solution

  • This is more concise:

    for (const val of someArray[0].properties || []) {
  // some processing
}

    Basically, if someArray[0].properties is undefined, the empty array is used instead of it throwing an error.