console.log(t);//Uncaught ReferenceError: t is not defined

//一般地，使用try-catch语句来捕获错误
try{
  t;
}catch(ex){
  console.log(ex.message);//t is not defined 
  console.log(ex.name);//ReferenceError
}

try{
  t;
}catch(ex){
  console.log(ex.stack);//@file:///D:/wamp/www/form.html:12:2
} 

new Error();
new Error(message);  
//一般地，使用throw语句来抛出错误
throw new Error('test');
//Uncaught Error: test
throw new Error();//Uncaught Error

function UserError(message) {
  this.message = message;
  this.name = "UserError";
}
UserError.prototype = new Error();
UserError.prototype.constructor = UserError;
throw new UserError("errorMessage");//Uncaught UserError: errorMessage

Error();
Error(message);  

throw Error('test');//Uncaught Error: test
throw Error();//Uncaught Error

var test = new Error('testError');
console.log(test.toString());//'Error: testError'

Error
EvalError(eval错误)
RangeError(范围错误)
ReferenceError(引用错误)
SyntaxError(语法错误)
TypeError(类型错误)
URIError(URI错误)

new Array(-1);//Uncaught RangeError: Invalid array length
new Array(Number.MAX_VALUE);//Uncaught RangeError: Invalid array length

(1234).toExponential(21);//Uncaught RangeError: toExponential() argument must be between 0 and 20
(1234).toExponential(-1);////Uncaught RangeError: toExponential() argument must be between 0 and 20

a;//Uncaught ReferenceError: a is not defined
1++;//Uncaught ReferenceError: Invalid left-hand side expression in postfix operation

//变量名错误
var 1a;//Uncaught SyntaxError: Unexpected number

// 缺少括号
console.log 'hello');//Uncaught SyntaxError: Unexpected string

var o = new 10;//Uncaught TypeError: 10 is not a constructor
alert('name' in true);//Uncaught TypeError: Cannot use 'in' operator to search for 'name' in true
Function.prototype.toString.call('name');//Uncaught TypeError: Function.prototype.toString is not generic

decodeURI('%2');// URIError: URI malformed

//DOM0级
window.onerror = function(message,url,line){
  alert(message);
}
//DOM2级
window.addEventListener("error",function(message,url,line){
  alert(message);
});

//控制台显示错误消息
window.onerror = function(message,url,line){
  alert(message);
  return false;
}
a;

//控制台不显示错误消息
window.onerror = function(message,url,line){
  alert(message);
  return true;
}
a;

var image = new Image();
image.src = 'smilex.gif';
image.onerror = function(e){
  console.log(e);
}

throw 12345;
throw 'hello world';
throw true;
throw {name: 'javascript'};

throw new Error('something bad happened');

throw new SyntaxError('I don\'t like your syntax.');
throw new TypeError('what type of variable do you take me for?');
throw new RangeError('sorry,you just don\'t have the range.');
throw new EvalError('That doesn\'t evaluate.');
throw new URIError('URI, is that you?');
throw new ReferenceError('you didn\'t cite your references properly');

function CustomError(message){
  this.name = 'CustomError';
  this.message = message;
}
CustomError.prototype = new Error();
throw new CustomError('my message');

try{
  //通常来讲，这里的代码会从头到尾而不会产生任何问题
  //但有时会抛出一个异常，要么是由throw语句直接抛出，要么通过调用一个方法间接抛出
}catch(e){
  //当且仅当try语句块抛出了异常，才会执行这里的代码
  //这里可以通过局部变量e来获得对Error对象或者抛出的其他值的引用
  //这里的代码块可以基于某种原因处理这个异常，也可以忽略这个异常，还可以通过throw语句重新抛出异常
}finally{
  //不管try语句是否抛出了异常，finally里的逻辑总是会执行，终止try语句块的方式有：
  //1、正常终止，执行完语句块的最后一条语句
  //2、通过break、continue或return语句终止
  //3、抛出一个异常，异常被catch从句捕获
  //4、抛出一个异常，异常未被捕获，继续向上传播
}

try{
  q;
}catch(error){
  alert(error.message);//q is not defined
}

//Uncaught SyntaxError: Unexpected token )
try{
  q;
}catch(){
  alert(error.message);
}

function throwIt(exception) {
 try {
  throw exception;
 } catch (e) {
  console.log('Caught: '+ e);
 }
}

throwIt(3);// Caught: 3
throwIt('hello');// Caught: hello
throwIt(new Error('An error happened'));// Caught: Error: An error happened

try{
 throw "出错了";
} catch (e) {
 console.log(111);
}
console.log(222);
// 111
// 222

try {
 foo.bar();
} catch (e) {
 if (e instanceof EvalError) {
  console.log(e.name + ": " + e.message);
 } else if (e instanceof RangeError) {
  console.log(e.name + ": " + e.message);
 }
 // ...
}

//由于没有catch语句块，所以错误没有捕获。执行finally代码块以后，程序就中断在错误抛出的地方
function cleansUp() {
 try {
  throw new Error('出错了……');
  console.log('此行不会执行');
 } finally {
  console.log('完成清理工作');
 }
}
cleansUp();
// 完成清理工作
// Error: 出错了……

function testFinnally(){
  try{
    return 2;
  }catch(error){
    return 1;
  }finally{
    return 0;
  }
}
testFinnally();//0

var count = 0;
function countUp() {
 try {
  return count;
 } finally {
  count++;
 }
}
countUp();// 0
console.log(count);// 1

function f() {
 try {
  console.log(0);
  throw "bug";
 } catch(e) {
  console.log(1);
  return true; // 这句原本会延迟到finally代码块结束再执行
  console.log(2); // 不会运行
 } finally {
  console.log(3);
  return false; // 这句会覆盖掉前面那句return
  console.log(4); // 不会运行
 }
 console.log(5); // 不会运行
}
var result = f();
// 0
// 1
// 3

console.log(result);// false

try{
  throw new Error();//抛出错误
}catch(e){
  console.log(e);//Error(…)
}
console.log(e);//Uncaught ReferenceError: e is not defined

function concat(str1,str2,str3){
  var result = str1 + str2;
  if(str3){ //绝对不要这样
    result += str3;
  }
  return result;
}

function concat(str1,str2,str3){
  var result = str1 + str2;
  if(typeof str3 == 'string'){ //更合适
    result += str3;
  }
  return result;
}

//不安全的函数，任何非数组值都会导致错误
function reverseSort(values){
  if(values){
    values.sort();
    values.reverse();
  }
}

//不安全的函数，任何非数组值都会导致错误
function reverseSort(values){
  if(values != null){
    values.sort();
    values.reverse();
  }
}

//不安全的函数，任何非数组值都会导致错误
function reverseSort(values){
  if(typeof values.sort == 'function'){
    values.sort();
    values.reverse();
  }
}

//安全，非数组值被忽略
function reverseSort(values){
  if(values instanceof Array){
    values.sort();
    values.reverse();
  }
}

//错误
http://www.yourdomain.com/?redir=http://www.sometherdomain.com?a=b&c=d
//针对'redir='后面的所有字符串调用encodeURIComponent()就可以解决这个问题
http://www.yourdomain.com/?redir=http:%3A%2F%2Fwww.sometherdomain.com%3Fa%3Db%26c%3Dd