新手入门：掌握JS入门的几大小技巧

前端入门需要了解的几个js小知识，比如找出总和、最小值、最大值、声明和初始化数组、filter过滤出数组中虚假值等等。

1、reduce找出总和、最小值和最大值

//reduce函数
const array  = [5,4,7,8,9,2];
//求和
array.reduce((a,b) => a+b); // 输出: 35
//找出最大
array.reduce((a,b) => a>b?a:b); // 输出: 9
//找出最小
array.reduce((a,b) => a<b?a:b); // 输出: 2

2、声明和初始化数组

const array = Array(5).fill(''); 
// 输出
(5) ["", "", "", "", ""]

const matrix = Array(5).fill(0).map(()=>Array(5).fill(0)); 
// 输出
(5) [Array(5), Array(5), Array(5), Array(5), Array(5)]
0: (5) [0, 0, 0, 0, 0]
1: (5) [0, 0, 0, 0, 0]
2: (5) [0, 0, 0, 0, 0]
3: (5) [0, 0, 0, 0, 0]
4: (5) [0, 0, 0, 0, 0]
length: 5

3、sort()和reverse()对字符串、数字或对象数组进行排序

//排序数字数组
const array  = [40, 100, 1, 5, 25, 10];
array.sort((a,b) => a-b);
// 输出
(6) [1, 5, 10, 25, 40, 100]

array.sort((a,b) => b-a);
// 输出
(6) [100, 40, 25, 10, 5, 1]

//排序字符串数组
const stringArr = ["Joe", "Kapil", "Steve", "Musk"]
stringArr.sort();
// 输出
(4) ["Joe", "Kapil", "Musk", "Steve"]

stringArr.reverse();
// 输出
(4) ["Steve", "Musk", "Kapil", "Joe"]

//对象数组排序
const objectArr = [
  { first_name: 'Lazslo', last_name: 'Jamf'     },
  { first_name: 'Pig',    last_name: 'Bodine'   },    
  { first_name: 'Pirate', last_name: 'Prentice' }
];
objectArr.sort((a, b) => a.last_name.localeCompare(b.last_name));
// 输出
(3) [{…}, {…}, {…}]
0: {first_name: "Pig", last_name: "Bodine"}
1: {first_name: "Lazslo", last_name: "Jamf"}
2: {first_name: "Pirate", last_name: "Prentice"}
length: 3

filter过滤出数组中虚假值

const array = [3, 0, 6, 7, '', false];
array.filter(Boolean);
// 输出
(3) [3, 6, 7]

删除重复值

const array  = [5,4,7,8,9,2,7,5];
array.filter((item,idx,arr) => arr.indexOf(item) === idx);
// or
const nonUnique = [...new Set(array)];
// 输出: [5, 4, 7, 8, 9, 2]

对各种条件使用逻辑运算符

function doSomething(arg1){ 
    arg1 = arg1 || 10; 
// 如果尚未设置，则将 arg1 设置为 10 作为默认值
return arg1;
}
 
let foo = 10;  
foo === 10 && doSomething(); 
// is the same thing as if (foo == 10) then doSomething();
// 输出: 10

foo === 5 || doSomething();
// is the same thing as if (foo != 5) then doSomething();
// 输出: 10

合并多个对象

const user = { 
 name: '小李', 
 gender: '一级'
 };
const college = { 
 primary: '大专', 
 secondary: 'A级'
 };
const skills = { 
 programming: '12', 
 swimming: '32', 
 sleeping: 'aa'
 };

const summary = {...user, ...college, ...skills};

Math.random()打乱数组

const list = [1, 2, 3, 4, 5, 6, 7, 8, 9];
list.sort(() => {
    return Math.random() - 0.5;
});
// 输出
(9) [2, 5, 1, 6, 9, 8, 4, 3, 7]

空合并运算符 (??)

const foo = null ?? 'my school';
// 输出: "my school"

const baz = 0 ?? 42;
// 输出: 0

单行回文检查

function checkPalindrome(str) {
  return str == str.split('').reverse().join('');
}
checkPalindrome('naman');
// 输出: true

将Object属性转成属性数组

使用Object.entries(),Object.keys()和Object.values()
const obj = { a: 1, b: 2, c: 3 };

Object.entries(obj);
// 输出
(3) [Array(2), Array(2), Array(2)]
0: (2) ["a", 1]
1: (2) ["b", 2]
2: (2) ["c", 3]
length: 3

Object.keys(obj);
(3) ["a", "b", "c"]

Object.values(obj);
(3) [1, 2, 3]

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