CODEWITHSUNDEEP
javascriptfunctionloopsrecursion
Autumn
Autumn

Reputation: 223

Javascript - deepEqual Comparison and Recursion

I'm teaching myself JavaScript, and I'm stuck on the following problem from Eloquent JavaScript:

Write a function, deepEqual, that takes two values and returns true only if they are the same value or are objects with the same properties whose values are also equal when compared with a recursive call to deepEqual. To find out whether to compare two things by identity (use the === operator for that) or by looking at their properties, you can use the typeof operator. If it produces "object" for both values, you should do a deep comparison. But you have to take one silly exception into account: by a historical accident, typeof null also produces "object".

My question: Why does console.log(deepEqual(obj, {here: {is: "an"}, object: 2})) come out as false when a[key] is { is: 'an' } and b[key] is { is: 'an' } but true when that code is substituted with !deepEqual(a[key], b[key])?

The code:

function deepEqual(a, b){
    if (a === b) {
        return true;
    } 
    else if (typeof a== typeof b && !(a===null ||b===null)){
        for(var key in b){
            for(key in a){
                if(! (key in a)){
                    return false;
                } 
                else if (a[key] !== b[key]){
                    return false;
                }
                else 
                    return true;
            }
        }
    }
  else
      return false;
}

var obj = {here: {is: "an"}, object: 2};
console.log(deepEqual(obj, {here: {is: "an"}, object: 2}));

Upvotes: 0

Views: 1466

Answers (1)

Justin Niessner
Justin Niessner

Reputation: 245419

Because a[key] and b[key] are both Objects, you need to use deepEquals on them as well.

Currently, you're not calling deepEquals recursively, so there's no way that will happen.

Upvotes: 1

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