// Create simple observable that emits three values const myObservable = of(1, 2, 3); // or from([1,2,3])
// Create observer object const myObserver = { next: x => console.log('Observer got a next value: ' + x), error: err => console.error('Observer got an error: ' + err), complete: () => console.log('Observer got a complete notification'), };
// Execute with the observer object myObservable.subscribe(myObserver); // Logs: // Observer got a next value: 1 // Observer got a next value: 2 // Observer got a next value: 3 // Observer got a complete notification
Perform a side effect for every emission on the source Observable, but return an Observable that is identical to the source.对源可观察对象的每个‘发射’应用一个副作用，但仍然返回与源相同的可观察对象
The lastValueFrom is almost exactly the same as toPromise() meaning that it will resolve with the last value that has arrived when the Observable completes, but with the difference in behavior when Observable completes without emitting a single value. When Observable completes without emitting, toPromise() will successfully resolve with undefined (thus the return type change), while the lastValueFrom will reject with the EmptyError. Thus, the return type of the lastValueFrom is Promise, just like toPromise() had in RxJS 6.lastValueFrom几乎与toPromise() 一个意思，在Observable complete的时候，lastValueFrom会带着Observable最后一个产生的值resolve，但是不同之处在于Observable不带值complete的情况下。 当Observable不产生值并且complete时，toPromise方法会成功resolve为undefined（也就是返回类型改变了，不再是T），但是lastValueFrom会带着EmptyErrorreject。因此，就如同在RxJS 6里一样，它的返回类型是Promise。
However, you might want to take the first value as it arrives without waiting an Observable to complete, thus you can use firstValueFrom. The firstValueFrom will resolve a Promise with the first value that was emitted from the Observable and will immediately unsubscribe to retain resources. The firstValueFrom will also reject with an EmptyError if the Observable completes with no values emitted.然而，你可能不等Observable complete，想要使用其第一个生产的值，因此可以用firstValueFrom。firstValueFrom会将Observable第一个生产的值resolve并且立刻unsubscribe保存该值。firstValueFrom也会在Observable没有值产生而complete的情况下带着 EmptyErrorreject。
GYP is short for ‘Generate Your Projects’，顾名思义，GYP工具用于生成在相应平台上的项目，如在windows平台上生成Visual Studio解决方案(.sln), Mac下则是XCode项目配置以及Scons工具。
node-gyp is a cross-platform command-line tool written in Node.js for compiling native addon modules for Node.js. It contains a fork of the gyp project that was previously used by the Chromium team, extended to support the development of Node.js native addons.
@{ // html标签 <div></div> var str = "abc"; // 下面会输出：this is a mail：dxl0321@qq.com, this is var: abc,this is mail@str,this is @； @: this is a mail：dxl0321@qq.com, this is var: @str,this is mail@str,this is @@； // 下面输出abc @str }
Function.prototype.bind = function (context) { // 调用 bind 的不是函数，需要抛出异常 if (typeof this !== "function") { throw new Error("Function.prototype.bind - what is trying to be bound is not callable"); } // this 指向调用者 var self = this; // 实现第2点，因为第1个参数是指定的this,所以只截取第1个之后的参数 var args = Array.prototype.slice.call(arguments, 1); // 创建一个空对象 var fNOP = function () {}; // 实现第3点,返回一个函数 var fBound = function () { // 实现第4点，获取 bind 返回函数的参数 var bindArgs = Array.prototype.slice.call(arguments); // 然后同传入参数合并成一个参数数组，并作为 self.apply() 的第二个参数 return self.apply(this instanceof fNOP ? this : context, args.concat(bindArgs)); // 注释1 } // 注释2 // 空对象的原型指向绑定函数的原型 fNOP.prototype = this.prototype; // 空对象的实例赋值给 fBound.prototype fBound.prototype = new fNOP(); return fBound; }
style=function(){this.x="";this.y="";} // 构造函数style style.prototype.addA=function(){ this.A='A' return this } style.prototype.addB=function(){ this.B='B' return this } style.prototype.addC=function(){ this.C='C' return this } // test xxx=new style() xxx.addA() xxx.addB().addC()
Garbage Collection
游离dom
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let root=document.getElementById("root") for(let i=0;i<2000;i++){ let div=document.createElement("div") root.appendChild(div) } document.body.removeChild(root)
function debounce(fn, wait){ let timeout return function(...args){ clearTimeout(timeout) timeout = setTimeout(()=> { fn.apply(this, args) }, wait) } }
事实上带有 this 的函数在使用生命周期钩子的vue/react组件中可能并不好用，应在组件范围声明timer, 在响应函数中clear并重新赋值
注意组件unmount时清理timer避免泄露
节流
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var throttle = function(delay, action){ // 这里是个全局变量 var last = 0 return function(){ var curr = new Date() if (curr - last > delay){ action.apply(this, arguments) last = curr } } }
