在JavaScript中实现Promise对象
class Promise2 { #status = 'pending' constructor(fn){ this.q = [] const resolve = (data)=>{ this.#status = 'fulfilled' const f1f2 = this.q.shift() if(!f1f2 || !f1f2[0]) return const x = f1f2[0].call(undefined, data) if(x instanceof Promise2) { x.then((data)=>{ resolve(data) }, (reason)=>{ reject(reason) }) }else { resolve(x) } } const reject = (reason)=>{ this.#status = 'rejected' const f1f2 = this.q.shift() if(!f1f2 || !f1f2[1]) return const x = f1f2[1].call(undefined, reason) if(x instanceof Promise2){ x.then((data)=>{ resolve(data) }, (reason)=>{ reject(reason) }) }else{ resolve(x) } } fn.call(undefined, resolve, reject) } then(f1, f2){ this.q.push([f1, f2]) } } const p = new Promise2(function(resolve, reject){ setTimeout(function(){ reject('出错') },3000) }) p.then( (data)=>{console.log(data)}, (r)=>{console.error(r)} )