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closure.js
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83 lines (73 loc) · 2.17 KB
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// Complete the following functions.
const counter = () => {
let count = 0;
return () => {
count++;
return count;
};
};
// const myCounter = counter();
// console.log(myCounter());
// console.log(myCounter());
// console.log(myCounter());
// console.log(myCounter());
// console.log(myCounter());
// console.log(myCounter());
// Return a function that when invoked increments and returns a counter variable.
// Example: const newCounter = counter();
// newCounter(); // 1
// newCounter(); // 2
const counterFactory = (() => {
let pcounter = 0;
function changeBy(val) {
pcounter += val;
}
return {
increment: () => {
changeBy(1);
},
decrement: () => {
changeBy(-1);
},
value: () => {
return pcounter;
}
};
})();
// console.log(counterFactory.value()); // logs 0
// counterFactory.increment();
// counterFactory.increment();
// console.log(counterFactory.value()); // logs 2
// counterFactory.decrement();
// console.log(counterFactory.value()); //1
// 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.
const limitFunctionCallCount = (cb, n) => {
let timesInvoked = 0;
return (...args) => {
if (timesInvoked === n) {
return null;
}
timesInvoked++;
return cb(...args);
};
};
// Should return a function that invokes `cb`.
// The returned function should only allow `cb` to be invoked `n` times.
/* STRETCH PROBLEM */
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.
};
/* eslint-enable no-unused-vars */
module.exports = {
counter,
counterFactory,
cacheFunction,
limitFunctionCallCount,
};