Throttle

Throttle depending on function arguments.

Installation

npm install --save @ambassify/throttle

Usage

const throttle = require('@ambassify/throttle');

const throttledFunction = throttle(<function-to-throttle>, <timeout>, [<cache-key-resolver> | <options>]);

throttledFunction.clear(<...args>);

throttle

• function-to-throttle: The function to which access should be throttled, will be called at most once during timeout period for the same cache-key (by default the first argument to this function).
• timeout: During this period only one call to function-to-throttle will be allowed with the same cache-key (in milliseconds).
• cache-key-resolver: This function generates the cache-key used as index into the cache. The resolver receives all of the same arguments as function-to-throttle. Default: The value of the first argument.
• options:
  • resolver: See cache-key-resolver argument
  • cache: A custom cache instance. It should implement the Map method interface of clear, delete, get, has, and set.
  • onCached: A callback that gets passed the cache item when a new item is cached.
  • maxSize: Shortcut to using LruCache with this maxSize value.
  • rejectFailedPromise: If true will not cache promises resulting in rejection.

.clear

• When invoked without any arguments the entire result cache is cleared.
• When arguments are supplied they are passed to cache-key-resolver to resolve the cache key to remove from cache.

CacheItem

CacheItems are exposed through the onCached callback that can be specified in the throttle options.

• key: The cache key for this item
• value: The cached value for this item
• clear: A method to clear this item from cache.
• ttl(timeout): A method to adjust the timeout of the cache item. Pass the new timeout in milliseconds.

Example

const throttle = require('@ambassify/throttle');

let example = 0;
function myFunction(input) {
    // Do some slow operation with a different result based on input
    example += input;
    return example;
}

// Allow `myFunction` to be called once every 2 seconds for each different `input`.
const myThrottledFunction = throttle(myFunction, 2000);


myThrottledFunction(1); // 1
myThrottledFunction(1); // 1
myThrottledFunction(1); // 1

// Wait for 2 seconds

myThrottledFunction(1); // 2
myThrottledFunction(1); // 2
myThrottledFunction(1); // 2

const conditionalThrottleFunction = throttle(myFunction, 2000, {
    onCached: function(item) {
        // Only cache results for large values of input
        if (item.key < 10)
            item.clear();
    }
}

conditionalThrottleFunction(1); // 1
conditionalThrottleFunction(1); // 2
conditionalThrottleFunction(1); // 3

conditionalThrottleFunction(20); // 23
conditionalThrottleFunction(20); // 23

Caches

This library currently provides one custom caching implementation you can use for the cache option.

LruCache

This cache implementation lets you specifiy a maximum size and will evict the least recently used items in cache when the cache overflows.

new LruCache(options)

• options:
  • maxSize: The maximum amount of items to keep in cache

Example

const throttle = require('@ambassify/throttle');
const LruCache = require('@ambassify/throttle/cache/lru');

function myFunction(input) {}

/**
 * Allow `myFunction` to be called once every 2 seconds for each different `input`
 * unless it is called more than 20 times with different `input` values. In that
 * case, it drops the cache item for the least recently used `input`
 */
const myThrottledFunction = throttle(myFunction, 2000, {
    cache: new LruCache({ maxSize: 20 })
});

Contributing

If you have some issue or code you would like to add, feel free to open a Pull Request or Issue and we will look into it as soon as we can.

License

We are releasing this under a MIT License.

About us

If you would like to know more about us, be sure to have a look at our website, or our Twitter accounts @Ambassify, Sitebase, JorgenEvens.