Promise

1.Interface:

prototype:

• then
• catch

static method:

• all
• race
• resolve
• reject

2.usage:

create Promise instance

var a=new Promise(function(res,rej){setTimeout(function(){res("succ-a");},2000);})//succ in the future
var b=new Promise(function(res,rej){setTimeout(function(){rej("fail-b");},2000);})//fail in the future
var c=new Promise(function(res,rej){setTimeout(function(){res("succ-c");},2000);})//succ in the future

then

a.then(function(val){console.log(val);},function(reason){console.log(reason);});//output:"succ-a"

catch

b.then(function(val){console.log(val);}).catch(function(reason){console.log(reason);});//output:"fail-b"

then chain

a.then(function(val){console.log(val);return "succ-a2";}).then(function(val){console.log(val);});//output:"succ-a","succ-a2"

then nest

a.then(function(val){console.log(val);return c.then(function(value){console.log(value);return "nest";});}).then(function(val){console.log(val);});//output:"succ-a","succ-c","nest"

all

var d1=new Promise(function(res,rej){setTimeout(function(){res("d1");},1000);})
var d2=new Promise(function(res,rej){setTimeout(function(){res("d2");},2000);})
var d3=new Promise(function(res,rej){setTimeout(function(){res("d3");},4000);})
var e=Promise.all([d1,d2,d3]);
e.then(function(val){console.log(val);});//output:["d1","d2","d3"]

race

var f1=new Promise(function(res,rej){setTimeout(function(){res("f1");},1000);})
var f2=new Promise(function(res,rej){setTimeout(function(){res("f2");},2000);})
var f3=new Promise(function(res,rej){setTimeout(function(){res("f3");},4000);})
var g=Promise.race([f1,f2,f3]);
g.then(function(val){console.log(val);});//output:"f1"  

3.analysis:

Example:x_promise.then(F1,F2).then(F3,F4).[---].then(Fm,Fn). *x_promise: a promise which is async. *chain: promise(x_promise)->promise(F1/2)->promise(F3/4)...->promise(Fm/n) *promise_Holder: an empty promise returned by then immediately.In the example-- x_promise.then(F1,F2).In chain. *promise_air: a promise returned by F1/2();Not in chain. *placeholder: a property of promise_air; It refers to promise_Holder. *promise_air.placeholder=promise_Holder.