我应该多彻底地检查 JavaScript 中可能出现的错误？

Question

I've difficulties to understand how far should I normally go with checking and validating data I operate in my code. I'm not even saying about user-input data here, I'm just saying about my own data, the data I know the structure of. For example, I might have some basic function like this:

let someData = [object];

someFunction(newData) {
  let newSet = newData.frequency[0];
  someData.dataset.chart.data[0].frequency = newSet;
}

Let's say I have someData variable that is used by a chart, and then I also have a function that simply updates the chart data with a new one. newData comes from my database (when user adjust filters and apply them) and someData is the default, initial data everyone sees. Now, my problem is... I foresee the following events:

1. Someone might change someData using Developers Console, so this variable will no longer hold an object, or won't have properties I address in my code, so it will lead to errors and break my logic entirely.

2. Someone might call someFunction directly (using console again) with very random data as argument, and this, again, will lead to errors.

3. Maybe newData received from DB will be somewhat wrong due to some errors on my side or anything, or maybe initial someData will fail initialising (cause it's initialised through a function as well and relies on third party.JS file that also might fail to load one day).

And I'm not even sure I've foreseen all possible events. So my code turns from what you saw above to something "tedious" (in my opinion) like this:

let someData = [object];

someFunction(newData) {
  let newSet = typeof newData === "object" &&
               newData.frequency ?
               newData.frequency[0] : undefined;
  let oldSet = typeof someData === "object" &&
               someData.dataset &&
               someData.dataset.chart &&
               someData.dataset.chart.data && 
               someData.dataset.chart.data[0] ?
               someData.dataset.chart.data[0].frequency : undefined;
  // Since using length on undefined will lead to an error, I've to check the type too
  if (Array.isArray(newSet) && newSet.length === 5 && oldSet) {
    oldSet = newSet;
  } else {
    throw Error("Dataset update has failed.");
  }
}

And even this doesn't guarantee that the newSet of data is the data I expect to see, because maybe I was looking for [1,2,3,4,5] and user managed to insert ["a","b","c","d","e"] via his console and so on. It feels like I can refine this endlessly and it will never be bulletproof plus eventually it's starting to get complicated to understand my own code, that the only thing I wanted to do is to changed old data with the new data. At this point I'm feeling like I'm doing it all wrong. Coding takes way more time and I'm not even sure I'm doing it for good, but at the same time I can't feel the limit when to stop over-validating my code. Please advise.

Answer 1

I would just stick with user input validation. Out of that, it's their problem if they want to screw you things with developper tools. Anyway, those would only stay on their side.

What's important is the validation on your server. The client side input validation is just to make sure everything put by regular user is error free before processing. It also save useless send to server. The server must redo the validation and more because of those screwed people.