implement promise

tPromise.js

class tPromise {
	constructor(fn){
		this.status = "pedding"
		this._queue = []
		this._catch = ()=>{ console.error("unhandle tPromise error") }
        	fn.call(this, this.resolve.bind(this), this.reject.bind(this))
	}

	resolve(data){
		this.status = "resolved";
        	this.data = data;
		if(this._queue.length > 0){
			let task = this._queue.shift();
			let res = task(this.data)
			// if respond is tPromise type, then transfer current then queue and catch function to new tPromise
			if(typeof res === 'object' && res.__proto__.constructor === tPromise){
				res._queue = this._queue
				res._catch = this._catch
				return res
			}
		}
		return this
	}

	reject(error){
		this._catch(error)
		this.status = "rejected"
		return this;
	}

	then(fn){
		if(this.status === "resolved"){
			return fn.call(this, this.data)
		}else if(this.status === "rejected"){
			this.catch(this.error)
			return this
		}
		// if the promise is resolved in async function. Keep chaining
		this._queue.push(fn.bind(this))
		return this
	}

	catch(fn){
		this._catch = fn.bind(this)
		return this
	}
}