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62 lines (56 loc) · 1.76 KB
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// Complete the following functions.
const counter = () => {
// Return a function that when invoked increments and returns a counter variable.
// Example: const newCounter = counter();
// newCounter(); // 1
// newCounter(); // 2
let count = 0;
return function () {
return count += 1;
};
};
const counterFactory = () => {
// Return an object that has two methods called `increment` and `decrement`.
// `increment` should increment a counter variable in closure scope and return it.
// `decrement` should decrement the counter variable and return it.
let count = 0;
const obj = {};
obj.increment = () => {
return count += 1;
};
obj.decrement = () => {
return count -= 1;
};
return obj;
};
const limitFunctionCallCount = (cb, n) => {
// Should return a function that invokes `cb`.
// The returned function should only allow `cb` to be invoked `n` times.
let callCount = 0;
return (...args) => {
callCount++;
if (n >= callCount) return cb(...args);
return null;
};
};
const cacheFunction = (cb) => {
// 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.
const cache = {};
return (input) => {
if (Object.prototype.hasOwnProperty.apply(cache, [input])) return cache[input];
cache[input] = cb(input);
return cache[input];
};
};
/* eslint-enable no-unused-vars */
module.exports = {
counter,
counterFactory,
cacheFunction,
limitFunctionCallCount
};