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callbacks.js
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87 lines (60 loc) · 2.39 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 will use the given `items` array and a variety of callbacks.
// Note how callbacks can be declared separately, or inlined.
// TEST 1 (inlined callback):
firstItem(items, item => console.log(`I love my ${item}!`));
// "I love my Pencil!"
// TEST 2 (declaring callback before hand):
function logExorbitantPrice(article) {
console.log(`this ${article} is worth a million dollars!`);
};
firstItem(items, logExorbitantPrice);
// "this Pencil is worth a million dollars!"
*/
function getLength(arr, cb) {
// getLength passes the length of the array into the callback.
cb(arr.length);
}
getLength([1,2,3],console.log);
function last(arr, cb) {
// last passes the last item of the array into the callback.
cb(arr[arr.length -1]);
}
last([1,2,3],console.log);
function sumNums(x, y, cb) {
// sumNums adds two numbers (x, y) and passes the result to the callback.
cb(x + y);
}
sumNums(1, 2, console.log);
function multiplyNums(x, y, cb) {
// multiplyNums multiplies two numbers and passes the result to the callback.
cb(x * y);
}
multiplyNums(1, 2, console.log);
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.
cb(list.indexOf(item) >= 0);
}
contains(10, [1,2,3], console.log);
/* 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.
cb(array.filter((item, index, array) => array.indexOf(item) === index));
}
removeDuplicates([1,1,2,3,4,4,4,5], console.log);