考查跨域JSONP[JavaScript] 纯文本查看 复制代码 function fn({ip}) {[/b] console.log(ip); //
}
function jsonp(cb, domain) {
const script = document.createElement('script');
script.src = `[url]https://api.asilu.com/ip/?callback=[/url]${cb}&ip=${domain}`;
document.querySelector('head').appendChild(script);
}
// 获取百度IP
jsonp('fn', 'www.baidu.com');
考查 ES6数组去重
[JavaScript] 纯文本查看 复制代码 function deleteDuplicate(arr) {
const map = new Map();
arr.forEach( value => map.set(value, value) );
return Array.from( map.values() ); // return [ ...map.values() ];
}
const arr = [NaN, 1, [1], [1], 1, '1', 4, 1, 2, 4, 5, 5, NaN, NaN, null, null, undefined, undefined];
deleteDuplicate( arr );
// [NaN, 1, Array(1), Array(1), "1", 4, 2, 5, null, undefined]
// Map 的遍历顺序就是插入顺序
[JavaScript] 纯文本查看 复制代码 function deleteDuplicate(arr) {
const set = new Set( arr );
return Array.from( set ); // return [ ...set ];
}
deleteDuplicate( arr );
//[NaN, 1, Array(1), Array(1), "1", 4, 2, 5, null, undefined]
Promise.all
[JavaScript] 纯文本查看 复制代码 Promise._all = function (promises) {
return new Promise(function(resolve, reject) {
if (!Array.isArray(promises)) {
return reject(new TypeError('arguments must be an array'));
}
const len = promises.length;
let cnt = 0;
let res = [];
for(let i = 0; i < len; i++) {
Promise
.resolve(promises[i])
.then(function(value) {
cnt++;
res[i] = value;
if (cnt === len) {
return resolve(res);
}
}, function(reason) {
return reject(reason);
});
}
});
};
Promise._all([1,2,3,4]);
// Promise {<resolved>: Array(4)}
Promise._all([1,2,3,4]).then(res => console.log(res));
// [1, 2, 3, 4]
Promise._all([1,2,3,Promise.reject('error')]);
// Promise {<rejected>: "error"}
Promise._all([1,2,3,Promise.reject('error')]).catch(reason => console.log(reason));
// error
考查设计模式订阅发布模式mitt：极简事件监听[JavaScript] 纯文本查看 复制代码 function mitt(all/*: EventHandlerMap*/) {[/size][/font][/color][/align] all = all || Object.create(null);
return {
on(type/*: string*/, handler/*: EventHandler*/) {
(all[type] || (all[type] = [])).push(handler);
},
off(type/*: string*/, handler/*: EventHandler*/) {
if (all[type]) {
all[type].splice(all[type].indexOf(handler) >>> 0, 1);
}
},
emit(type/*: string*/, evt/*: any*/) { // * 表示订阅所有事件消息
(all[type] || []).slice().map((handler) => { handler(evt); });
(all['*'] || []).slice().map((handler) => { handler(type, evt); });
}
};
}
const m = mitt();
m.on('hello', (name) => console.log('hello ' + name));
m.emit('hello', 'world');
考查算法深拷贝Vuex版[JavaScript] 纯文本查看 复制代码 /**[/size][/font][/color][/align] * Get the first item that pass the test
* by second argument function
*
* @param {Array} list
* @param {Function} f
* @return {*}
*/
export function find (list, f) {
return list.filter(f)[0]
}
/**
* Deep copy the given object considering circular structure.
* This function caches all nested objects and its copies.
* If it detects circular structure, use cached copy to avoid infinite loop.
*
* @param {*} obj
* @param {Array<Object>} cache
* @return {*}
*/
export function deepCopy (obj, cache = []) {
// just return if obj is immutable value
if (obj === null || typeof obj !== 'object') {
return obj
}
// if obj is hit, it is in circular structure
const hit = find(cache, c => c.original === obj)
if (hit) {
return hit.copy
}
const copy = Array.isArray(obj) ? [] : {}
// put the copy into cache at first
// because we want to refer it in recursive deepCopy
cache.push({
original: obj,
copy
})
Object.keys(obj).forEach(key => {
copy[key] = deepCopy(obj[key], cache)
})
return copy
}
DFS 全排列
[JavaScript] 纯文本查看 复制代码 输入 `abc`
输出
abc
acb
bac
bca
cab
cba
[JavaScript] 纯文本查看 复制代码 const str = 'abc';
const len = str.length;
const flag = [];
const res = [];
DFS(0);
// cur 表示第 cur 位取得字符
// 每一位有 len 种取法
function DFS(cur) {
if(cur === len)
return console.log(res.join(''));
for(let i = 0; i < len; i++) {
if(!flag[i]) {
res[cur] = str[i];
flag[i] = true;
DFS(cur + 1);
flag[i] = false;
}
}
}
快排
[JavaScript] 纯文本查看 复制代码 function swap(arr, i, j) {
if(i === j) return;
let tmp = arr[i];
arr[i] = arr[j];
arr[j] = tmp;
}
function quicksort(arr, s, e) {
if( s >= e ) return;
const r = s + Math.floor( (e - s) / 2 );
// 选取中间位r(也可以随机)放在首位
swap(arr, s, r);
// 找选取的数应该在数组中的位置
// 小于则表示位置挪后一位
let m = s, j = s + 1;
for(; m < e && j < e; j++) {
if(arr[j] < arr[s]) {
swap(arr, ++m, j);
}
}
// 找到 r 的序位
swap(arr, s, m);
// 递归排序左左右两边
quicksort(arr, s, m);
quicksort(arr, m + 1, e);
}
let arr = [2, 7, 3, 4, 1, 8, 6];
quicksort(arr, 0, arr.length);
考查正则、replace 技巧数钱格式化
[JavaScript] 纯文本查看 复制代码 '99999999'.replace(/\d{1,3}(?=(\d{3})+$)/g, '$&,');
// antd 的例子
'99999999'.replace(/\B(?=(\d{3})+(?!\d))/g, ',');
// 非正则版
function money(str) {
const len = str.length;
let start = len % 3 || 3;
let arr = [str.slice(0, start)];
while(start < len) {
arr.push( str.slice(start, start + 3) );
start += 3;
}
return arr.join(',')
}
首尾去空格[JavaScript] 纯文本查看 复制代码 ' 12 34 5 6 '.replace(/^\s+|\s+$/g, '');
相邻字符去重[JavaScript] 纯文本查看 复制代码 'aaabbbcdfgghhjjkkk'.replace(/([A-Za-z]{1})(\1)+/g, '$1');
单词首字母大写[JavaScript] 纯文本查看 复制代码 ' hi man good luck '.replace(/\w+/g, function(word) { [/b] return word.substr(0,1).toUpperCase() + word.substr(1);
});
转自：https://juejin.im/post/5e71b2dbf265da5757049549
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