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challenges.js
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104 lines (95 loc) · 2.99 KB
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/* ======================== CallBacks Practice ============================ */
const each = (elements, cb) => {
// Iterates over a list of elements, yielding each in turn to the `cb` function.
// This only needs to work with arrays.
for (let i = 0; i < elements.length; i++) {
cb(elements[i], i);
}
return elements;
};
const map = (elements, cb) => {
// Produces a new array of values by mapping each value in list through a transformation function (iteratee).
// Return the new array.
const arr = [];
for (let i = 0; i < elements.length; i++) {
arr.push(cb(elements[i]));
}
return arr;
};
/* ======================== Closure Practice ============================ */
const limitFunctionCallCount = (cb, n) => {
// Should return a function that invokes `cb`.
// The returned function should only allow `cb` to be invoked `n` times.
let counter = 0;
return (...args) => {
if (counter === n) {
return null;
}
counter++;
return cb(...args);
};
};
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 y0 => {
if (cache[y0] === undefined) {
cache[y0] = cb;
return cache[y0](y0);
}
return cache[y0];
};
};
/* eslint-enable no-unused-vars */
/* ======================== Recursion Practice ============================ */
const reverseStr = str => {
// reverse str takes in a string and returns that string in reversed order
// The only difference between the way you've solved this before and now is that you need to do it recursivley!
if (str === '') {
return '';
}
return reverseStr(str.substr(1)) + str.charAt(0);
};
const checkMatchingLeaves = obj => {
// return true if every property on `obj` is the same
// otherwise return false
const testKey = obj[Object.keys(obj)[0]];
const x = (obj2, testCase) => {
const objKey = Object.keys(obj2);
for (let i = 0; i < objKey.length; i++) {
if (typeof obj2[objKey[i]] === 'object') return x(obj2[objKey[i]], testCase);
if (testKey !== obj2[objKey[i]]) {
return false;
}
}
return true;
};
return x(obj, testKey);
};
const flatten = elements => {
// Flattens a nested array (the nesting can be to any depth).
// Example: flatten([1, [2], [3, [[4]]]]); => [1, 2, 3, 4];
let newArr = [];
for (let i = 0; i < elements.length; i++) {
if (Array.isArray(elements[i])) {
newArr = newArr.concat(flatten(elements[i]));
} else {
newArr.push(elements[i]);
}
}
return newArr;
};
module.exports = {
each,
map,
limitFunctionCallCount,
cacheFunction,
reverseStr,
checkMatchingLeaves,
flatten
};