详解JavaScript错误捕获

try{
    //code....
}catch(err){
    //error handling
}finally{
    //no matter what happens in the try/catch (error or no error), this code in the finally statement should run. 
}

try{
    {{{{{{{
}catch(err){
    console.error(err)
}
//引擎在‘parse-time'出错，导致无法理解代码，因此无法捕捉

try{
    setTimeout(function(){
        undefinedVariable;
    },1000)
}catch(err){
    console.error(err)
}
//setTimeout的回调函数执行时，引擎已经离开try...catch结构

function test(){
  try {
    return 1;
  } catch(error) {
    return 2;
  } finally {
    return 3;
  }
}
console.log(test());
//3

try {
  lalala; // error, variable is not defined!
} catch (err) {
  alert(err.name); // ReferenceError
  alert(err.message); // lalala is not defined
  alert(err.stack); // ReferenceError: lalala is not defined at (...call stack)

  // Can also show an error as a whole
  // The error is converted to string as "name: message"
  alert(err); // ReferenceError: lalala is not defined
}

let json = '{ "age": 30 }'; 
try{
  let user = JSON.parse(json);  
  alert( user.name );
} catch (err) {
  console.error('JSON Error:'+err);
}

let json = '{"age":30}'
try{
  let user =  JSON.parse(json);
  alert(user.name)
}catch(err){
   if(err instanceof SyntaxError){
       console.error('JSON Error:'+err);
   }
   else throw err;
}

try{
    new Promise((resolve,reject)=>{
        throw new Error('promise error')
    }).catch(()=>{
        //错误在最近的onreject回调被捕获
        console.error(err);
    })
}catch(err){
    //永远不会执行，promise吞掉error
    console.error(err);
}

try{
    new Promise((resolve,reject)=>{
        resolve();
    }).then(()=>{
        throw new Error('promise then error');
    }).catch((err){
        console.error(err);
    })
}catch(err){
    //地球毁灭之前都不会执行
    console.error(err)
}

try {
    new Promise((resolve, reject) => {
        throw new Error('promise error')
    }).then((ret) => {
        //错误没有处理，失效
        console.log('then1:' + ret)
    }).catch((err) => {
        //错误处理了，后序正常
        console.error(err);
        return 'handled'
    }).then((ret) => {
        //正常执行
        console.log('then2' + ret);
    })
} catch (err) {
    //同样的，人类毁灭之前都不会执行
    console.error(err)
}

// Error:promise error
//then2handled