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Copy patharrays.js
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84 lines (73 loc) · 2.29 KB
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// Complete the following functions.
// These functions only need to work with arrays.
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.
// based off http://underscorejs.org/#each
for (let i = 0; i < elements.length; i++) {
cb(elements[i], i);
}
};
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 newArray = [];
for (let i = 0; i < elements.length; i++) {
newArray[i] = cb(elements[i]);
}
return newArray;
};
const reduce = (elements, cb, memo) => {
// Combine all elements into a single value going from left to right.
// Elements will be passed one by one into `cb`.
// `memo` is the starting value. If `memo` is undefined then make `elements[0]` the initial value.
let i = 0;
if (memo === undefined) {
memo = elements[0];
i++;
}
for (; i < elements.length; i++) {
memo = cb(memo, elements[i]);
}
return memo;
};
const find = (elements, cb) => {
// Look through each value in `elements` and pass each element to `cb`.
// If `cb` returns `true` then return that element.
// Return `undefined` if no elements pass the truth test.
for (let i = 0; i < elements.length; i++) {
if (cb(elements[i])) {
return elements[i];
}
}
return undefined;
};
const filter = (elements, cb) => {
// Similar to `find` but you will return an array of all elements that passed the truth test
// Return an empty array if no elements pass the truth test
const answer = [];
for (let i = 0; i < elements.length; i++) {
if (cb(elements[i])) {
answer.push(elements[i]);
}
}
return answer;
};
const flatten = (elements) => {
// Flattens a nested array (the nesting can be to any depth).
// Example: flatten([1, [2], [3, [[4]]]]); => [1, 2, 3, 4];
// x should return an array (5ms)
// ✕ should return a flattened array when given a nested array (1ms)
// ✕ should return a flattened array regardless of how deep the array nesting is (2ms)
const flatArray = [];
return flatArray;
};
/* eslint-enable no-unused-vars, max-len */
module.exports = {
each,
map,
reduce,
find,
filter,
flatten
};