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closure.js
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76 lines (69 loc) · 2.15 KB
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// Complete the following functions.
const counter = () => {
let currentCount = 0;
return function () {
return ++currentCount;
};
// Return a function that when invoked increments and returns a counter letiable.
// Example: const newCounter = counter();
// newCounter(); // 1
// newCounter(); // 2
};
const counterFactory = () => {
let count = 0;
const counterObject = {};
counterObject.count = 0;
counterObject.increment = function () {
return ++count;
};
counterObject.decrement = function () {
return --count;
};
return counterObject;
// Return an object that has two methods called `increment` and `decrement`.
// `increment` should increment a counter letiable in closure scope and return it.
// `decrement` should decrement the counter letiable and return it.
};
const limitFunctionCallCount = (cb, n) => {
let callCount = 0;
return (...args) => {
callCount++;
if (callCount <= n) {
return cb(...args);
}
return null;
};
return funcCall;
// Should return a function that invokes `cb`.
// The returned function should only allow `cb` to be invoked `n` times.
};
/* STRETCH PROBLEM */
const cacheFunction = (cb) => {
const cacheObject = {
cachedArgs: [],
results: [],
};
return (args) => {
for (let i = 0; i < cacheObject.cachedArgs.length; i++) {
if (cacheObject.cachedArgs.includes(args)) {
return cacheObject.results[cacheObject.cachedArgs.indexOf(args)];
}
}
cacheObject.results.push(cb(args));
cacheObject.cachedArgs.push(args);
return cacheObject.results[cacheObject.results.length - 1];
};
};
// Should return a funciton that invokes `cb`.
// A cache (object) should be kept in closure scope.
// The cache should keep track of all arguments have been used to invoke this function.
// If the returned function is invoked with arguments that it has already seen
// then it should return the cached result and not invoke `cb` again.
// `cb` should only ever be invoked once for a given set of arguments.
/* eslint-enable no-unused-lets */
module.exports = {
counter,
counterFactory,
cacheFunction,
limitFunctionCallCount,
};