JavaScript高階函數(shù)的詳細介紹（附代碼）

sayHi = (name) => `Hi, ${name}!`;
result = sayHi('User');
console.log(result); // 'Hi, User!'

double = (x) => x * 2;
result = double(4);
console.log(result); // 8

getClearance = (allowed) => allowed ?
 'Access granted' :
 'Access denied';
result1 = getClearance(true);
result2 = getClearance(false);
console.log(result1); // 'Access granted'
console.log(result2); // 'Access denied'

getFirstName = (obj) => obj.firstName;
result = getFirstName({
 firstName: 'Yazeed'
});
console.log(result); // 'Yazeed'

len = (array) => array.length;
result = len([1, 2, 3]);
console.log(result); // 3

isEven = (num) => num % 2 === 0;
result = [1, 2, 3, 4].filter(isEven);
console.log(result); // [2, 4]

add = (x) => (y) => x + y;

result = add(10)(20);
console.log(result); // 30

add10 = add(10);
result = add10(20);
console.log(result); // 30

users = [{
 name: 'Yazeed',
 age: 25
}, {
 name: 'Sam',
 age: 30
}, {
 name: 'Bill',
 age: 20
}];

getName = (user) => user.name;
usernames = [];
for (let i = 0; i < users.length; i++) {
 const name = getName(users[i]);
 usernames.push(name);
}
console.log(usernames);
// ["Yazeed", "Sam", "Bill"]

usernames = users.map(getName);
console.log(usernames);
// ["Yazeed", "Sam", "Bill"]

startsWithB = (string) => string
 .toLowerCase()
 .startsWith('b');
namesStartingWithB = [];
for (let i = 0; i < users.length; i++) {
 if (startsWithB(users[i].name)) {
 namesStartingWithB.push(users[i]);
 }
}
console.log(namesStartingWithB);
// [{ "name": "Bill", "age": 20 }]

namesStartingWithB = users
 .filter((user) => startsWithB(user.name));
console.log(namesStartingWithB);
// [{ "name": "Bill", "age": 20 }]