Category: JavaScript

Sometimes, we may run into the ‘TypeError: can’t access dead object’ when we’re developing JavaScript apps.

In this article, we’ll look at how to fix the ‘TypeError: can’t access dead object’ when we’re developing JavaScript apps.

Fix the ‘TypeError: can’t access dead object’ When Developing JavaScript Apps

To fix the ‘TypeError: can’t access dead object’ when we’re developing JavaScript apps, we should make sure we check that the object is still available before accessing it.

To do this, we can use the Component.utils.isDeadWrapper method:

if (Components.utils.isDeadWrapper(window)) {
  // dead
}

We can also try to catch exceptions from trying to accessing unavailable objects:

try {
  String(window);
}
catch (e) {
  console.log("window is dead");
}

Conclusion

To fix the ‘TypeError: can’t access dead object’ when we’re developing JavaScript apps, we should make sure we check that the object is still available before accessing it.

Sometimes, we may run into the ‘TypeError: X.prototype.y called on incompatible type’ when we’re developing JavaScript apps.

In this article, we’ll look at how to fix the ‘TypeError: X.prototype.y called on incompatible type’ when we’re developing JavaScript apps.

Fix the ‘TypeError: X.prototype.y called on incompatible type’ When Developing JavaScript Apps

To fix the ‘TypeError: X.prototype.y called on incompatible type’ when we’re developing JavaScript apps, we should make sure that we’re calling Function.prototype.call, Function.prototype.apply, or Function.prototype.bind with a this value that is expected.

For instance, if we have:

const mySet = new Set;
['bar', 'baz'].forEach(mySet.add);

then we’ll get the error since the this value in mySet.add isn’t mySet.

To fix this, we write:

const mySet = new Set;
['bar', 'baz'].forEach(mySet.add.bind(mySet));

to call bind with mySet to set mySet as the value of this in the mySet.add method.

Conclusion

To fix the ‘TTypeError: X.prototype.y called on incompatible type’ when we’re developing JavaScript apps, we should make sure that we’re calling Function.prototype.call, Function.prototype.apply, or Function.prototype.bind with a this value that is expected.

Sometimes, we may run into the ‘TypeError: Reduce of empty array with no initial value’ when we’re developing JavaScript apps.

In this article, we’ll look at how to fix the ‘TypeError: Reduce of empty array with no initial value’ when we’re developing JavaScript apps.

Fix the ‘TypeError: Reduce of empty array with no initial value’ When Developing JavaScript Apps

To fix the ‘TypeError: Reduce of empty array with no initial value’ when we’re developing JavaScript apps, we should make sure that we’re calling the Array.prototype.reduce method with an initial value.

For instance, if we have:

const ints = [0, -1, -2, -3, -4, -5];
ints.filter(x => x > 0)
    .reduce((x, y) => x + y)

then we get the error since we didn’t pass in a 2nd argument to reduce.

So the x parameter in the reduce callback is set to undefined and the callback fails to run.

To fix this, we write:

const ints = [0, -1, -2, -3, -4, -5];
ints.filter(x => x > 0)
    .reduce((x, y) => x + y, 0)

to pass in a 2nd argument to reduce.

Then x is set to 0 and that’s returned since filter returned an empty array.

Conclusion

To fix the ‘TypeError: Reduce of empty array with no initial value’ when we’re developing JavaScript apps, we should make sure that we’re calling the Array.prototype.reduce method with an initial value.

Sometimes, we may run into the ‘TypeError: More arguments needed’ when we’re developing JavaScript apps.

In this article, we’ll look at how to fix the ‘TypeError: More arguments needed’ when we’re developing JavaScript apps.

Fix the ‘TypeError: More arguments needed’ When Developing JavaScript Apps

To fix the ‘TypeError: More arguments needed’ when we’re developing JavaScript apps, we should make sure that we’re passing in all the required arguments to the Object.create and Object.setPrototypeOf methods.

Different variations of this error includes:

TypeError: argument is not an Object and is not null (Edge)
TypeError: Object.create requires at least 1 argument, but only 0 were passed
TypeError: Object.setPrototypeOf requires at least 2 arguments, but only 0 were passed
TypeError: Object.defineProperties requires at least 1 argument, but only 0 were passed

For instance, if we have:

const obj = Object.create();
const obj = Object.setPrototypeOf({});

In the first line, we didn’t pass in any arguments into Object.create which are expected.

And in the 2nd line, we’re missing the 2nd argument.

To fix this, we write:

const obj = Object.create(null);
const obj = Object.setPrototypeOf({}, null);

Conclusion

To fix the ‘TypeError: More arguments needed’ when we’re developing JavaScript apps, we should make sure that we’re passing in all the required arguments to the Object.create and Object.setPrototypeOf methods.

Sometimes, we may run into the ‘TypeError: ‘x’ is not iterable’ when we’re developing JavaScript apps.

In this article, we’ll look at how to fix the ‘TypeError: ‘x’ is not iterable’ when we’re developing JavaScript apps.

Fix the ‘TypeError: ‘x’ is not iterable’ When Developing JavaScript Apps

To fix the ‘TypeError: ‘x’ is not iterable’ when we’re developing JavaScript apps, we should make sure we’re using the for-of loop on an object that’s iterable like an array, set, map, string, etc.

On Firefox and Chrome, the error message for this error is TypeError: 'x' is not iterable.

On Chrome, the message TypeError: 'x' is not a function or its return value is not iterable is also sometimes shown for this error.

For instance, if we try to iterate through a non-iterable object:

const obj = { 'France': 'Paris', 'England': 'London' };
for (let p of obj) { 
  // ...
}

then we’ll get this error.

Instead, we can use Object.entries to get the key-value pair array and we can use the for-of loop with that:

for (const [country, capital] of Object.entries(obj)) {
  console.log(country, capital);
}

If we’re iterating over a generator function, we should make sure we call it before we iterate through the returned items.

For instance, the following will throw this error:

function* generate(a, b) {
  yield a;
  yield b;
}

for (const x of generate) {
  console.log(x);
}

The function itself isn’t iterable, so we get this error.

Instead, we write:

function* generate(a, b) {
  yield a;
  yield b;
}

for (const x of generate(1, 2)) {
  console.log(x);
}

to iterated through the returned items.

Conclusion

To fix the ‘TypeError: ‘x’ is not iterable’ when we’re developing JavaScript apps, we should make sure we’re using the for-of loop on an object that’s iterable like an array, set, map, string, etc.

On Firefox and Chrome, the error message for this error is TypeError: 'x' is not iterable.

On Chrome, the message TypeError: 'x' is not a function or its return value is not iterable is also sometimes shown for this error.