data-structurespriority-queueheap# How to use built in priority queue in javascript?

How can we use built in priority queue in javascript

In chrome I am not able to run built in pq in javascript

Solution

There is nothing "built in" in JavaScript that bears the name priority queue. The native thing that comes closest is a plain object with *array-index* keys.

That comes with some limitations:

- The keys of the priority queue have to be unsigned integers in the 32-bit range
- The priority queue cannot hold two items with the same key unless you add additional logic to deal with that.

Here is how that would work:

```
function pqInsert(pq, key, value) {
if (String(Math.abs(+key | 0)) != String(key)) throw "Key must be unsigned 32 bit integer";
if (pq[key] !== undefined) throw "Duplicate key";
pq[key] = value;
}
function pqLeastKey(pq) {
for (const key in pq) { // Iterate numeric keys in order
return key; // Exit in first iteration
}
}
function pqExtract(pq) {
const key = pqLeastKey(pq);
const value = pq[key]; // Get value of least key
delete pq[key]; // Remove it
return [key, value];
}
const pq = {};
// I/O handling
const [keyInput, valueInput, addButton, removeButton, br, output] =
document.body.children;
addButton.onclick = () => {
pqInsert(pq, keyInput.value, valueInput.value);
keyInput.value = valueInput.value = "";
output.textContent = JSON.stringify(pq, null, 2);
}
removeButton.onclick = () => {
[keyInput.value, valueInput.value] = pqExtract(pq);
output.textContent = JSON.stringify(pq, null, 2);
};
```

`input { width: 5em }`

```
Key: <input type="number" min="0"> Value: <input> <button>Add</button>
<button>Extract minimum</button><br>
Queue: <pre>{}</pre>
```

That's as close as you can get to a *native* priority queue behaviour in JavaScript. Alternatively, you can of course add a library, or throw your own implementation of a priority queue. For instance, at Efficient way to implement Priority Queue in Javascript? you'll find some implementations. I also posted my heap implementation there.

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