memoization-behavior.html

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<script>
  window.Biddle = window.Biddle || {};
/**
`Biddle.MemoizationBehavior` allows you to define a computed property
as memoizable (http://en.wikipedia.org/wiki/Memoization) with `_memoizeComputed`
or more generally memoize any given function with `_memoize`

To implement a computed property as memoizable in the simplest fashion (although
this is a trivial example, you would likely only want to memoize expensive functions)

    behaviors: [
        Biddle.MemoizationBehavior,
    ],

    properties: {
        firstName: String,
        lastName: String,
        fullName: {
            type: String,
            computed: '_memoizeComputed("fullName", firstName, lastName)'
            method: '_getFullName'
        }
    },

    _getFullName: function (first, last) {
        return first + ' ' + last;
    }

Given that the default hash function is `JSON.stringify` which may be inappropriate
for object/array parameters you may wish to override the default hashing method
for a specific property.

    properties: {
        foo: Object,
        bar: Object,
        foobar: {
            type: String,
            computed: '_memoizeComputed("fullName", foo, bar)'
            method: '_computeFoobar',
            hashFn: (foo, bar) => foo.id + ':' + bar.id
        }
    },

To generally memoize any function you may do the following

    var someValue = this._memoize(this.someExpensiveFunction)(arg2, arg2, arg3);

Cache invalidation happens manually with the `_invalidateMemoizeCache` method

    var foo = this._memoize(this.bar)('Hello');
    // ...
    this._invalidateMemoizeCache(this.bar);

@demo demo/demo.html
@polymerBehavior
*/
  Biddle.MemoizationBehavior = {

    /**
     * Default method to create the hash to key a value in the function's cache
     * @type {!Function}
     */
    _defaultMemoizeHash: (...args) => JSON.stringify(args),

    /**
     * Memoize a given function
     * @param {!Function} func   Function to memoize
     * @param {Function}  hashFn Method to create the hash key, defaults to `_defaultMemoizeHash`
     * @return {Function}
     */
    _memoize: function (func, hashFn) {
      hashFn = hashFn || this._defaultMemoizeHash;
      return function (...args) {
        var key = '' + hashFn.apply(this, args);
        func.cache = func.cache || {};
        if (!(key in func.cache)) {
          func.cache[key] = func.apply(this, args);
        }
        return func.cache[key];
      };
    },

    /**
     * Memoize a given computed function
     * @param {!String} property Name of property being computed (camelCase)
     * @param {...*}    args     Any args to pass to compute function as normal
     * @return {*}
     */
    _memoizeComputed: function (property, ...args) {
      var propertyDef = this.properties[property];
      var hashFn = propertyDef.hashFn || this._defaultMemoizeHash;
      return this._memoize(this[propertyDef.method], hashFn).apply(this, args);
    },

    /**
     * Invalidate the cache for a given method
     * @param {String} method
     */
    _invalidateMemoizeCache: function (method) {
      method.cache = {};
    }
  };
</script>