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76 changes: 76 additions & 0 deletionsarrays.js
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// Complete the following functions.
// These functions only need to work with arrays.
// Do NOT use the built in array methods to solve these. forEach, map, reduce, filter, includes, etc.
// You CAN use concat, push, pop, etc. but do not use the exact method that you are replicating
// You can use the functions that you have already written to help solve the other problems

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.
// You should also pass the index into `cb` as the second argument
// 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.push(cb(elements[i]));
}
return newArray;
};

const reduce = (elements, cb, startingValue) => {
// Combine all elements into a single value going from left to right.
// Elements will be passed one by one into `cb` along with the `startingValue`.
// `startingValue` should be the first argument passed to `cb` and the array element should be the second argument.
// `startingValue` is the starting value. If `startingValue` is undefined then make `elements[0]` the initial value.
let memo = (startingValue === undefined) ? elements[0] : startingValue;
let i = (startingValue === undefined) ? 1 : 0;
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 newArr = [];
for (let i = 0; i < elements.length; i++) {
if (cb(elements[i])) newArr.push(elements[i]);
}
return newArr;
};

/* STRETCH PROBLEM */

const flatten = (elements) => {
// 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,
};
65 changes: 65 additions & 0 deletionscallbacks.js
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/* eslint-disable */

const firstItem = (arr, cb) => {
// firstItem passes the first item of the given array to the callback function.
cb(arr[0]);
};

const getLength = (arr, cb) => {
// getLength passes the length of the array into the callback.
cb(arr.length);
};

const last = (arr, cb) => {
// last passes the last item of the array into the callback.
const arrayLength = arr.length;
cb(arr[arrayLength - 1]);
};

const sumNums = (x, y, cb) => {
// sumNums adds two numbers (x, y) and passes the result to the callback.
const sum = x + y;
cb(sum);
};

const multiplyNums = (x, y, cb) => {
// multiplyNums multiplies two numbers and passes the result to the callback.
const sum = x * y;
cb(sum);
};

const contains = (item, list, cb) => {
// contains checks if an item is present inside of the given array/list.
// Pass true to the callback if it is, otherwise pass false.
for(let i = 0; i < list.length; i++){
if(item === list[i]) return cb(true);
}
return cb(false);
};

/* STRETCH PROBLEM */

const removeDuplicates = (array, cb) => {
// removeDuplicates removes all duplicate values from the given array.
// Pass the duplicate free array to the callback function.
// Do not mutate the original array.
const newArr = [];
for(let i = 0; i < array.length; i++){
contains(array[i], newArr, (isDuplicate) => {if(!isDuplicate) {
newArr.push(array[i]);
}
})
}
cb(newArr);
};

/* eslint-enable */
module.exports = {
firstItem,
getLength,
last,
sumNums,
multiplyNums,
contains,
removeDuplicates,
};
58 changes: 58 additions & 0 deletionsclosure.js
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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 tracker = 0;
return () => { return ++tracker; };
};

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 tracker = 0;
return {
increment: () => {
return ++tracker;
},
decrement: () => {
return --tracker;
},
};
};

const limitFunctionCallCount = (cb, n) => {
// Should return a function that invokes `cb`.
// The returned function should only allow `cb` to be invoked `n` times.
let i = 0;
return (...args) => {
if (i < n) {
i++;
return cb(...args);
}
return null;
};
};

/* 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,
};
82 changes: 82 additions & 0 deletionsobjects.js
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// Complete the following underscore functions.
// Reference http://underscorejs.org/ for examples.

const keys = (obj) => {
// Retrieve all the names of the object's properties.
// Return the keys as strings in an array.
// Based on http://underscorejs.org/#keys
const keyArray = [];
Object.keys(obj).forEach((key) => {
keyArray.push(key);
});
return keyArray;
};

const values = (obj) => {
// Return all of the values of the object's own properties.
// Ignore functions
// http://underscorejs.org/#values
return Object.values(obj);
};

const mapObject = (obj, cb) => {
// Like map for arrays, but for objects. Transform the value of each property in turn.
// http://underscorejs.org/#mapObject
keys(obj).forEach((key) => {
obj[key] = cb(obj[key]);
});
return obj;
};

const pairs = (obj) => {
// Convert an object into a list of [key, value] pairs.
// http://underscorejs.org/#pairs
const list = [];
keys(obj).forEach((key) => {
const pair = [];
pair.push(key);
pair.push(obj[key]);
list.push(pair);
});
return list;
};

/* STRETCH PROBLEMS */

const invert = (obj) => {
// Returns a copy of the object where the keys have become the values and the values the keys.
// Assume that all of the object's values will be unique and string serializable.
// http://underscorejs.org/#invert
const invertedObject = {};
keys(obj).forEach((key) => {
const keyHolder = key;
const valueHolder = obj[key];
invertedObject[valueHolder] = keyHolder;
});
return invertedObject;
};

const defaults = (obj, defaultProps) => {
// Fill in undefined properties that match properties on the `defaultProps` parameter object.
// Return `obj`.
// http://underscorejs.org/#defaults
keys(defaultProps).forEach((key) => {
if (obj[key] === undefined) {
keys(defaultProps).forEach((defaultKey) => {
if (defaultKey === key) obj[key] = defaultProps[defaultKey];
});
}
});
return obj;
};

/* eslint-enable no-unused-vars */

module.exports = {
keys,
values,
mapObject,
pairs,
invert,
defaults,
};
1 change: 1 addition & 0 deletionsscript.js
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console.log("Hello world!");
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