jQuery的未定义对象属性仍然会导致错误，即使不被调用

Question

I'm iterating through an api object and certain results do not have a specific attribute. I used this to make a placeholder if the attribute was missing:

if (data.track[i].image == undefined) {
    urlstring = "path/to/image";
} else {
  urlstring = data.track[i].image[4][0];
}

Unfortunately, I still get the error Uncaught TypeError: Cannot read property '0' of undefined , even though the else clause shouldn't trigger if the attribute is undefined.

Answer 1

Your problem is that data.track[i].image[4] is undefined while your code seems to expect an array.

You might use

if (data.track[i].image && data.track[i].image[4]) {
    urlstring = data.track[i].image[4][0];
} else {
    urlstring = "path/to/image";
}

Note: I assumed the mix between data.track[i] and data.toptracks.track[i] is an artefact of the question.