強制promise對象按順序執行

方法一

	new Promise(function(resolve){
		setTimeout(resolve(console.log("a")),600)
	}).then(new Promise(function(resolve){
		setTimeout(resolve(console.log("b")),700)
	})).then(new Promise(function(resolve){
		setTimeout(resolve(console.log("c")),200)
	}))

方法二

	var p1 = new Promise((resolve, reject) => { 
	  setTimeout(resolve(console.log("a")), 100); 
	}); 
	var p2 = new Promise((resolve, reject) => { 
	  setTimeout(resolve(console.log("b")), 600); 
	});
	var p3 = new Promise((resolve, reject) => {
	  setTimeout(resolve(console.log("c")), 100); 
	});
	var p4 = new Promise((resolve, reject) => {
	  setTimeout(resolve(console.log("d")), 300); 
	});
	
	
	Promise.all([p1, p2, p3, p4]).then(values => { 
	  console.log("ok");
	}, reason => {
	  console.log(reason)
	});