Breaking Down and Optimizing your Code with Destructuring and

Currently, I am performing some basic destructuring in Javascript:

//@flow
"use strict";

(function(){
    const {a,c} = check(true);
})();


function check(bool:boolean):{|a:string,c:string|}|{||}{
  if(bool){
    return { 
      a:"b",
      c:"d"
    };

  }
  else{
    return Object.freeze({});
  }
}

Despite this, Flow is presenting errors.

5:  const {a,c} = check(true);
           ^ property `a`. Property not found in
9: function check(bool:boolean):{|a:string,c:string|}|{||}{
                                                  ^ object type
5:  const {a,c} = check(true);
             ^ property `c`. Property not found in
9: function check(bool:boolean):{|a:string,c:string|}|{||}{
                                                      ^ object type

Try out the code on this web compiler link

What exactly is Flow looking for and how can these issues be resolved?

Answer №1

The check() function signature is not {a: string, c: string}. I made adjustments to your code to match this type and it resolved the issue.

//@flow
"use strict";

(function(){
    const {a,c} = check(true);
})();


function check(bool:boolean):{|a:string,c:string|}{
   if(bool){
      return { 
         a:"b",
         c:"d"
      };

   } else{
     return Object.freeze({a: "", c: ""});
   }
}

If this solution does not work for your specific use case, please let me know by leaving a comment.

Answer №2

One issue is that your function currently has a return type that can either be an empty object or in the form of {a: string, b: string}

function check(bool:boolean):{|a:string,c:string|}|{||}{

The "|" symbol represents OR, so in this case, your function's return type is either {|a: string, c: string|} OR {|}

Refer to:

When you destructure it in the following function

const {a,c} = check(true);

It attempts to access the properties a and c in an empty object, which triggers this warning because the check function might also return an empty object.

Resolution:

Assign some default values to variables a and c initially so that even if they are absent, they will still be initialized

(function(){
    const {a='',c=''} = check(true);
})();

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