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callbacks.js
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96 lines (71 loc) · 2.88 KB
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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"];
/*
// 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.length);
}
console.log(
getLength(items, length => `The length of the array is ${length}.`)
);
// ====================================================
function last(arr, cb) {
// last passes the last item of the array into the callback.
return cb(arr[arr.length - 1]);
}
console.log(last(items, last => `The last item is ${last}.`));
// ====================================================
function sumNums(x, y, cb) {
// sumNums adds two numbers (x, y) and passes the result to the callback.
let result = x + y;
return cb(result);
}
console.log(sumNums(4, 5, sum => `The sum is ${sum}.`));
// ====================================================
function multiplyNums(x, y, cb) {
// multiplyNums multiplies two numbers and passes the result to the callback.
let result = x * y;
return cb(result);
}
console.log(multiplyNums(2, 3, product => `The product is ${product}.`));
// ====================================================
function 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.
if (list.includes(item)) {
return cb(true);
} else {
return cb(false);
}
}
console.log(contains("Gum", items, cb => cb));
/* 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.
}