去重
const unique = (arr) => arr.reduce(
(acc, val) => (acc.indexOf(val) == -1 ? acc.push(val) : acc, acc), []);
const unique = (arr) => arr.filter((val,index)=>arr.indexOf(val)==index);
let arr = [1, 2, 1, 1, 2, 3, 3, 4, 1, 1, 2, 2, 5];
console.log(unique(arr));//[ 1, 2, 3, 4, 5 ]iterator 迭代器
Iterator接口主要为for of服务的,供for...of进行消费首先他作为一个对象,这个对象有一个
next方法,每次调用next方法都会返回一个结果值这个结果值是一个
object,包含两个属性,value和done
value表示具体的返回值,done是布尔类型的,表示集合是否遍历完成或者是否后续还有可用数据,有false,没有true代码实现
const getIterator = list => { let i = 0; return { next: () => ({ done: (i >= list.length), value: list[i++] }) } }; let a = getIterator([1, 2, 3]); console.log(a.next()); //{ done: false, value: 1 } console.log(a.next()); //{ done: false, value: 2 } console.log(a.next()); //{ done: false, value: 3 } console.log(a.next()); //{ done: true, value: undefined }给对象添加
Symbol.iterator属性,此属性指向一个迭代器方法,这个迭代器会返回一个特殊的对象-迭代器对象var arr=[100,200,300]; var iteratorObj= arr[Symbol.iterator]();//得到迭代器方法，返回迭代器对象 console.log(iteratorObj.next());判断对象是否是可迭代的
既然可迭代对象的规则必须在对象上部署
Symbol.iterator属性,可以判断对象是否为可迭代对象,const isIterable = obj => typeof obj[Symbol.iterator] === 'function';
解构
数组的元素是按次序排列的,变量的取值由位置决定的;
对象的属性没有次序,变量必须与属性同名,才能取到正确的值
let [a, b, c] = [1, 2, 3]; console.log(a, b, c);//1,2,3 let {age,name}={name:'zs', age: 12}; console.log(name, age);// 'zs' 12对象的解构
let {random}=Math; console.log(random() * 10);
前端大面试
http://bigerfe.com/trimStart trimEnd
trimStart 只清除头部的空格
trimEnd 只清楚尾部的空格
去重
const responseList = [
{ id: 1, a: 1 },
{ id: 2, a: 2 },
{ id: 3, a: 3 },
{ id: 1, a: 4 },
];
const result = responseList.reduce((acc, cur) => {
const ids = acc.map(item => item.id);
return ids.includes(cur.id) ? acc : [...acc, cur];
}, []);发现一个有趣的需求
const capitalizeHeadline = str => {
return str.split(' ').reduce((acc, val, index, array) => {
return acc + ((index == 0 || index == array.length - 1) ? val[0].toUpperCase() + val.substr(1) : val)+' ';
}, '')
};
console.log(capitalizeHeadline('abd sslsl dddd'));
// Abd sslsl Dddd 给数字添加千分位逗号
const transform = (num = 0) => {
let nums = num.toString();
let [num1, num2] = nums.split('.');
let a = num1.split('').reduceRight((acc, val, index) => {
return acc + ((index > 1 && index % 3 == 0) ? val + ',' : val);
}, '');
return a + (num2 ? '.' + num2 : '')
};
console.log(transform(123433434.1221));
// 434,334,321.1221ＣＳＳ灵感
https://chokcoco.github.io/CSS-Inspiration/#/./shadow/one-sided-shadow.md
leetCode121 买卖股票的最佳时机
const solution = nums => {
if (nums.length < 2) {
return 0
}
//最大值得初始化为0,最小值为第一个数,循环从1开始
let max = 0, min = nums[0], i = 0;
while (++i < nums.length) {
min = Math.min(min, nums[i]);
max = Math.max(max, nums[i] - min)
}
return max
};从排序数组中删去重复的项
const removeDuplicates = nums => {
if (nums.length < 2) {
return 0
}
let i = 0;
for (let j = 1; j < nums.length; j++) {
if (nums[i] != nums[j]) {
++i;
nums[i] = nums[j]
}
}
nums.length = i + 1;
return nums
};
const removeDuplicates = nums => nums.reduce((acc, val) =>
acc.indexOf(val) === -1 ? acc.concat(val) : acc
, []);反转字符串中的单词
const reverseWord = str => str.split(' ')
.reduce((acc, val) =>acc.concat( val.split('').reverse().join('') + ' ')
, '');
console.log(reverseWord('abc cdfg smd'));905. 按奇偶排序数组
const sortArray = arr => {
let a = 0, max = arr.length - 1, res = [];
for (let item of arr) {
if (item % 2 == 0) {
res[a++] = item
} else {
res[max--] = item
}
}
return res
};
console.log(sortArray([1, 2, 3, 4, 5, 6]));
// [ 2, 4, 6, 5, 3, 1 ]复习 && || !
! 取反
a||b a为真返回a a为假返回b
a&&b a为真返回b a为假返回a判断字符串或者数组是否唯一
const inUnique = str => {
let obj = {};
for (let item of str) {
if (obj[item]) {
return false
}
obj[item] = true
}
return true
};改变跑马灯的时间
$('.marquee-box').css('animation-duration','10s')数组转对象
Object.assign({}, [1, 2, 3, 4]);
// { '0': 1, '1': 2, '2': 3, '3': 4 }使得两个数之和等于目标值
const twoSum = (array, target) => {
for (let i = 0; i < array.length; i++) {
let a = array.indexOf(target - array[i]);
if (a > -1 && a != i) {
return [i, a]
}
}
return [-1, -1]
};
console.log(twoSum([1, 2, 3, 4, 5, 6], 3));