promise 特点总结

来源：互联网发布：软件测试原佩腾编辑：程序博客网时间：2024/04/19 16:48

(1)promise的resolve不支持第二个参数的传递(不是大问题)

process.stdin.setEncoding('utf8');let promise = new Promise(function(resolve, reject) {  process.stdin.on('readable', () => {    var chunk = process.stdin.read();    if (chunk !== null) {      if(chunk==1)      {        resolve({test1:'succ1',test2:'succ2'},{"resolve":resolve,"reject":reject});      }      else{        reject({test1:'error1',test2:'error2'},{"resolve":resolve,"reject":reject});      }      // process.stdout.write(`data: ${chunk}`);    }  });});promise.then(function(value1,status) {  console.log("succ第一次传递then的值是");  console.log(value1);  if(1)  {    console.log("第一次then(succ)里的status是");    console.log(status);    // 当reject，resolve作为第二个参数传递时会报出status==undefined的错误  }},function(value1,status){  console.log("err第一次传递then的值是");  console.log(value1);});promise.then(function(value1) {  console.log("succ第2次传递then的值是");  console.log(value1);},function(value1) {  console.log("err第2次传递then的值是");  console.log(value1);});

(2)promise 不支持第一个then之后的分支选择(是个大问题)

process.stdin.setEncoding('utf8');let promise = new Promise(function(resolve, reject) {  process.stdin.on('readable', () => {    var chunk = process.stdin.read();    if (chunk !== null) {      if(chunk==1)      {        resolve({test1:'succ1',test2:'succ2',"resolve":resolve,"reject":reject});      }      else{        reject({test1:'error1',test2:'error2',"resolve":resolve,"reject":reject});      }      // process.stdout.write(`data: ${chunk}`);    }  });});promise.then(function(value1) {  console.log("succ第一次传递then的值是");  console.log(value1);  if(1)  {    // 测试作为一个参数传递的情况     console.log("第一次传递then的reject是");     console.log(value1.reject);     value1.reject("then2");     //**分支选择错误**     //**走的仍然是"succ第2次传递then的值是"这个提示**  }},function(value1,status){  console.log("err第一次传递then的值是");  console.log(value1);});promise.then(function(value1) {  console.log("succ第2次传递then的值是");  console.log(value1);},function(value1) {  console.log("err第2次传递then的值是");  console.log(value1);});

(3) promise不支持return式的参数变化机制(小问题)

process.stdin.setEncoding('utf8');let promise = new Promise(function(resolve, reject) {  process.stdin.on('readable', () => {    var chunk = process.stdin.read();    if (chunk !== null) {      if(chunk==1)      {        resolve({test1:'succ1',test2:'succ2'},{"resolve":resolve,"reject":reject});      }      else{        reject({test1:'error1',test2:'error2'},{"resolve":resolve,"reject":reject});      }    }  });});promise.then(function(value1,status) {  console.log("succ第一次传递then的值是");  console.log(value1);  if(1)  {      // value1.test1="succthen";      // delete value1.test2;      // 直接在原有的resolve对象上修改生效      // return {"test1":"succthen"};      // 不支持返回新值的状态改变机制  }},function(value1,status){  console.log("err第一次传递then的值是");  console.log(value1);});promise.then(function(value1) {  console.log("succ第2次传递then的值是");  console.log(value1);},function(value1) {  console.log("err第2次传递then的值是");  console.log(value1);});

总结：
promise实用场景
这里写图片描述

一次分支决定一生
可以再向下传递中改变状态量

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