是否可以进行条件性销毁或回退？

Question

I have an object that has lots of deeply nested properties. I want to be able to access properties on "MY_KEY" (below), but if that doesn't exist then get "MY_OTHER_KEY". How can I accomplish that?

const {
  X: {
    Y: {
      MY_KEY: {
        Values: segments = []
      } = {}
    } = {}
  } = {}
} = segment;

Answer 1

You could achieve this using a temporal variable inside your destructuring assignment, something like this:

 function destructure(segments) { const { X: { Y: { MY_OTHER_KEY: _fallback_value = {}, MY_KEY: { Values: segment = [] } = _fallback_value, } = {}, } = {}, } = segments; return segment; } console.log(destructure({})); // [] console.log(destructure({X:{}})); // [] console.log(destructure({X:{Y:{MY_KEY:{Values:"A"}}}})); // A console.log(destructure({X:{Y:{MY_OTHER_KEY:{Values:"B"}}}})); // B console.log(destructure({X:{Y:{MY_OTHER_KEY:{Values:"C"}, MY_KEY:{Values:"D"}}}})); // D 

First of all, this kind of destructuring will attempt to extract the second key all the time, which might have some unintended implications, like a property getter for MY_OTHER_KEY will always run.

However I fail to see the beauty in it. Hiding some control flow inside destructuring is just confusing. I would rather suggest extracting the parent object and use regular property access on it:

 function destructure(segments) { const { X: { Y: nested = {}, } = {}, } = segments; const selected = nested.MY_KEY || nested.MY_OTHER_KEY || {}; const { Values: segment = [] } = selected; return segment; } console.log(destructure({})); // [] console.log(destructure({X:{}})); // [] console.log(destructure({X:{Y:{MY_KEY:{Values:"A"}}}})); // A console.log(destructure({X:{Y:{MY_OTHER_KEY:{Values:"B"}}}})); // B console.log(destructure({X:{Y:{MY_OTHER_KEY:{Values:"C"}, MY_KEY:{Values:"D"}}}})); // D 

Answer 2

Check if the target is defined

let {/* do destructuring stuff */}

if (MY_KEY === undefined) {
  // define `MY_OTHER_KEY` variable here
}

If you are trying to assign target to a different property if the previous target definition is undefined you can assign the variable at subsequent target definition

 const segment = {Y:123}; let or = "Y"; let X; ({X, X = X || segment[or]} = segment); console.log(X); 

Answer 3

While object destructuring is cool and new, it is not the best in all cases. May do:

try {   
  var segments = segment.X.Y.MY_KEY.Values;
} catch(e){
 //whatever
}