Difference between hasOwnProperty(propName) and hasOwnProperty("propName")

Question

Difference between hasOwnProperty(propName) and hasOwnProperty("propName")

After completing the challenge on Record Collection, I have come up with a functional solution.

I have a question about when to use quotes ("" or '') inside the propName for hasOwnProperty(propName). Can you explain when to use hasOwnProperty(propName) versus hasOwnProperty("propName")?

Below is my solution that works:

function updateRecords(id, prop, value) {
 if (prop != "tracks" && value != "") {
   collection[id][prop] = value;
 }
else if (prop === "tracks" && collection[id].hasOwnProperty("tracks") === false) {
 collection[id].tracks = [];
 collection[id].tracks.push(value);
}

 else if (prop ==="tracks" && value != ""){
   collection[id].tracks.push(value);
 }
else if (value === "") {
   delete collection[id][prop];
 }
  return collection;
}

Interestingly, changing hasOwnProperty("tracks") to hasOwnProperty(tracks) breaks the code. This is perplexing as the example I saw for hasOwnProperty(propName) did not include quotes and failed when quotes were added around propName.

I first learned about hasOwnProperty() from: Testing object for Properties.

javascript

Answer 1

Answer №1

It is crucial to utilize a string when checking for the existence of a property on an object. This is especially important when quotes are not used, as it signifies that a variable storing the property name as a string value must be used. This is unrelated to whether the variable shares the same name as the property. For instance, consider the following code snippet where properties are iterated over and checked for ownership within the object (excerpt taken from documentation on Object.prototype.hasOwnProperty):

var buz = {
  fog: 'stack'
};

for (var name in buz) {
  if (buz.hasOwnProperty(name)) {
    console.log('this is fog (' + 
      name + ') for sure. Value: ' + buz[name]);
  }
  else {
    console.log(name);
  }
}

As pointed out by @Gavin, the example demonstrates how the property name can be passed as a string instead of propname

Answer 2

It is crucial to utilize a string when checking for the existence of a property on an object. This is especially important when quotes are not used, as it signifies that a variable storing the property name as a string value must be used. This is unrelated to whether the variable shares the same name as the property. For instance, consider the following code snippet where properties are iterated over and checked for ownership within the object (excerpt taken from documentation on Object.prototype.hasOwnProperty):

var buz = {
  fog: 'stack'
};

for (var name in buz) {
  if (buz.hasOwnProperty(name)) {
    console.log('this is fog (' + 
      name + ') for sure. Value: ' + buz[name]);
  }
  else {
    console.log(name);
  }
}

As pointed out by @Gavin, the example demonstrates how the property name can be passed as a string instead of propname

Difference between hasOwnProperty(propName) and hasOwnProperty("propName")

Answer №1

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