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Copy patharrays.js
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82 lines (73 loc) · 2.16 KB
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// Complete the following functions.
// These functions only need to work with arrays.
const each = (elements, cb) => {
elements.forEach((element, i) => {
return cb(element, i);
});
return 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
};
const map = (elements, cb) => {
const newArray = elements.map((element) => {
return cb(element);
});
return newArray;
// Produces a new array of values by mapping each value in list through a transformation function (iteratee).
// Return the new array.
};
const reduce = (elements, cb, memo) => {
let i = 0;
if (!memo) {
memo = elements[0];
i++;
}
for (i; i < elements.length; i++) memo = cb(memo, elements[i]);
return 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.
const find = (elements, cb) => {
const finder = elements.find((e) => {
if (cb(e)) return e;
return undefined;
});
return finder;
// 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.
};
const filter = (elements, cb) => {
const arr = [];
elements.filter((e) => {
if (cb(e)) {
arr.push(e);
return arr;
} return [];
});
return arr;
// 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 flatten = (elements) => {
return elements.reduce((a, b) => {
if (Array.isArray(b)) {
return a.concat(flatten(b));
}
return a.concat(b);
}, []);
// a.concat(Array.isArray(b) ? flatten(b) : b), []});
// Flattens a nested array (the nesting can be to any depth).
// Example: flatten([1, [2], [3, [[4]]]]); => [1, 2, 3, 4];
};
/* eslint-enable no-unused-vars, max-len */
module.exports = {
each,
map,
reduce,
find,
filter,
flatten
};