要异步读取的变量的值

Question

我从注册表中读取值并将注册表中的值设置为代码中的变量。我看到从注册表中获取值是异步发生的。

我是来自 node 的 regedit 包。我试过用 setTimeout 代替 constructENVTable，但没用。请从 html 页面主体 onload

触发 note:mainfunc()

//declared globally
var regValue = "";

function mainfunc() {
  setRegistryValueForFirstTime();
  constructENVTable();
}

function setRegistryValueForFirstTime() {
  let path = "HKLM\....\Environment";
  regedit.list('HKLM\...\Environment', function(err, result) {
    try {
      regValue = result[path].values.XYZ.value;
      alert(regValue); //prints value correctly
      app.console.log("Registry value for ANSYS_LI is  already set");
    } catch (err) {
      app.console.log(err);
      app.console.log("setting up registry value");
      setRegistryValue();
    }
    alert(regValue); //doesn't print value
  });
}

  function constructENVTable() {
    alert(regValue); //doesn't print value
  }

Answer 1

为了简单起见，你可以运行函数一取值，然后在第二个函数中传递。

var regValue = "";

function mainfunc() {
  setRegistryValueForFirstTime();
}

function setRegistryValueForFirstTime() {
  let path = "HKLM\....\Environment";
  regedit.list('HKLM\...\Environment', function(err, result) {
    try {
      regValue = result[path].values.XYZ.value;
      app.console.log("Registry value for ANSYS_LI is  already set");
      constructENVTable(regValue); //prints value correctly
    } catch (err) {
      app.console.log(err);
      app.console.log("setting up registry value");
      setRegistryValue();
    }
  });
}

function constructENVTable(regValue) {
  alert(regValue); // get value here and alert it
}

Answer 2

您可以用 Promise 包装 regValue：

var regValue;

function mainfunc() {
    setRegistryValueForFirstTime();
    constructENVTable();
}

function setRegistryValueForFirstTime() {
    let path = "HKLM\....\Environment";
    regedit.list('HKLM\...\Environment', function (err, result) {
        try {
            regValue = new Promise(
                (resolve, reject) => resolve(result[path].values.XYZ.value)
            )

            app.console.log("Registry value for ANSYS_LI is  already set");
        } catch (err) {
            app.console.log(err);
            app.console.log("setting up registry value");
            setRegistryValue();
        }
        alert(regValue); //doesn't print value
    });
}

function constructENVTable() {
    // alert(regValue); //doesn't print value
    regValue.then(
        value => alert(value)
    )
}

要异步读取的变量的值

Value of a variable to be read asynchronously

javascript

regedit