// 第一种:Map记录
function quchong1(arr) {
const newArr = []
arr.reduce((pre, next) => {
if (!pre.has(next)) {
pre.set(next, 1)
newArr.push(next)
}
return pre
}, new Map())
return newArr
}
// 第二种:Set去重
function quchong2(arr) {
return [...new Set(arr)]
}
实现(a == 1 && a == 2 && a == 3)为true
// 第一种方法
var a = {
i: 1,
toString: function () {
return a.i++;
}
}
console.log(a == 1 && a == 2 && a == 3) // true
// 第二种方法
var a = [1, 2, 3];
a.join = a.shift;
console.log(a == 1 && a == 2 && a == 3); // true
// 第三种方法
var val = 0;
Object.defineProperty(window, 'a', {
get: function () {
return ++val;
}
});
console.log(a == 1 && a == 2 && a == 3) // true
var times = function() {
var timing = performance.timing;
var loadTime = timing.loadEventEnd - timing.navigationStart;//过早获取时,loadEventEnd有时会是0
if(loadTime <= 0) {
// 未加载完,延迟200ms后继续times方法,直到成功
setTimeout(function(){
times();
}, 200);
return;
}
var readyStart = timing.fetchStart - timing.navigationStart;
var redirectTime = timing.redirectEnd - timing.redirectStart;
var appcacheTime = timing.domainLookupStart - timing.fetchStart;
var unloadEventTime = timing.unloadEventEnd - timing.unloadEventStart;
var lookupDomainTime = timing.domainLookupEnd - timing.domainLookupStart;
var connectTime = timing.connectEnd - timing.connectStart;
var requestTime = timing.responseEnd - timing.requestStart;
var initDomTreeTime = timing.domInteractive - timing.responseEnd;
var domReadyTime = timing.domComplete - timing.domInteractive; //过早获取时,domComplete有时会是0
var loadEventTime = timing.loadEventEnd - timing.loadEventStart;
// 为console.table方法准备对象,包含耗时的描述和消耗的时间
var allTimes = [
{ "描述": "准备新页面时间耗时", "时间(ms)": readyStart },
{ "描述": "redirect 重定向耗时", "时间(ms)": redirectTime },
{ "描述": "Appcache 耗时", "时间(ms)": appcacheTime },
{ "描述": "unload 前文档耗时", "时间(ms)": unloadEventTime },
{ "描述": "DNS 查询耗时", "时间(ms)": lookupDomainTime },
{ "描述": "TCP连接耗时", "时间(ms)": connectTime },
{ "描述": "request请求耗时", "时间(ms)": requestTime },
{ "描述": "请求完毕至DOM加载", "时间(ms)": initDomTreeTime },
{ "描述": "解释dom树耗时", "时间(ms)": domReadyTime },
{ "描述": "load事件耗时", "时间(ms)": loadEventTime },
{ "描述": "从开始至load总耗时", "时间(ms)": loadTime }
];
console.table(allTimes);
}
window.onload = times;// onload时,触发times方法
// `a` 和 `b` 都是数组
const isEqual = (a, b) => JSON.stringify(a) === JSON.stringify(b);
// 或者
const isEqual = (a, b) => a.length === b.length &&
a.every((v, i) => v === b[i]);
// 事例
isEqual([1, 2, 3], [1, 2, 3]); // true
isEqual([1, 2, 3], [1, '2', 3]); // false
const getSelectedText = () => window.getSelection().toString();
var formatNumber = function(n) {
n = n.toString()
return n[1] ? n : '0' + n
// 或者 return ('0'+ n).slice(-2)
}
function getDistance(lng1, lat1, lng2, lat2) {
let alpha = (lat1 * Math.PI) / 180.0;
return Math.sqrt(Math.pow((lat1 - lat2) * 111.12, 2) + Math.pow((lng1 - lng2) * Math.cos(alpha) * 111.12, 2));
}