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callbacks.js
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// Create a higher order function and invoke the callback function to test your work. You have been provided an example of a problem and a solution to see how this works with our items array. Study both the problem and the solution to figure out the rest of the problems.
const items = ['Pencil', 'Notebook', 'yo-yo', 'Gum', 'Gum'];
/*
// GIVEN THIS PROBLEM:
function firstItem(arr, cb) {
// firstItem passes the first item of the given array to the callback function.
}
// SOLUTION:
function firstItem(arr, cb) {
return cb(arr[0]);
}
// NOTES ON THE SOLUTION:
// firstItem is a higher order function.
// It expects a callback (referred to as `cb`) as its second argument.
// To test our solution, we can use the given `items` array and a variety of callbacks.
// Note how callbacks can be declared separately, or inlined.
// TEST 1 (inlined callback):
const test1 = firstItem(items, item => `I love my ${item}!`);
console.log(test1); // "I love my Pencil!"
// TEST 2 (declaring callback before hand):
function logExorbitantPrice(article) {
return `this ${article} is worth a million dollars!`;
};
const test2 = firstItem(items, logExorbitantPrice);
console.log(test2); // "this Pencil is worth a million dollars!"
*/
function getLength(arr, cb) {
// getLength passes the length of the array into the callback.
return cb(arr);
}
const the_len = (arr) => { return arr.length; }
console.log(getLength(items, the_len));
function last(arr, cb) {
// last passes the last item of the array into the callback.
return cb(arr);
}
const last_item = (arr) => { return arr[arr.length - 1]; }
//const last_item = (arr) => { arr.slice(-1)[0]; }
console.log(last(items, last_item));
function sumNums(x, y, cb) {
// sumNums adds two numbers (x, y) and passes the result to the callback.
return cb(x,y);
}
const sum = (x,y) => { return x + y; }
console.log(sumNums(10, 5, sum));
function multiplyNums(x, y, cb) {
// multiplyNums multiplies two numbers and passes the result to the callback.
return cb(x, y);
}
const mult = (x,y) => { return x * y; }
console.log(multiplyNums(3, 5, mult));
function contains(element, arr, 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.
return cb(element, arr);
}
const is_it_in = (item, list) => { return list.includes(item); }
console.log(contains('Gum', items, is_it_in));
/* STRETCH PROBLEM */
function 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.
return cb(array);
}
const remove_dupes = (arr) => {
let newArray = [];
for (let i=0; i<arr.length; i++) {
if (newArray.includes(arr[i])) {
continue;
} else {
newArray.push(arr[i]);
}
};
return newArray;
}
console.log(removeDuplicates(items, remove_dupes));