Error object in JavaScript

Whenever any runtime error occurs in JavaScript, an Error object is raised. In many cases, we can also extend these standard Error objects to create our own custom Error objects. Properties

Error

The object has 2 properties

name

- Set or return the error name. Specifically, it returns the name of the constructor to which the error belongs. It has 6 different values ​​-

EvalError

, RangeError, ReferenceError, TypeError, SyntaxError , URIError. As we'll discuss later in this article, all error types inherit from Object-> Error-> RangeError.

message

-Set or return error message

Example

1. Common errors

We can use the

Error

object to create a new Error and then explicitly throw the error using the throw keyword.

try{
    throw new Error('Some Error Occurred!')
} 
catch(e){
    console.error('Error Occurred. ' + e.name + ': ' + e.message)
}

2. Handle specific error types

We can also use the following

instanceof

Keywords to handle specific error types.

try{
    someFunction()
} 
catch(e){
    if(e instanceof EvalError) {
    console.error(e.name + ': ' + e.message)
  } 
  else if(e instanceof RangeError) {
    console.error(e.name + ': ' + e.message)
  }
  // ... something else
}

3. Custom error types

We can also define our own by creating a class that inherits the

Error

object error type.

class CustomError extends Error {
  constructor(description, ...params) {
    super(...params)
    
    if(Error.captureStackTrace){
      Error.captureStackTrace(this, CustomError)
    }
    this.name = 'CustomError_MyError'
    this.description = description
    this.date = new Date()
  }
}
try{
  throw new CustomError('Custom Error', 'Some Error Occurred')
} 
catch(e){
  console.error(e.name)           //CustomError_MyError
  console.error(e.description)    //Custom Error
  console.error(e.message)        //Some Error Occurred
  console.error(e.stack)          //stacktrace
}

Browser Compatibility

Object type of Error

Now let us discuss the different error object types that can be used to handle different errors.

1. EvalError

Create an

error

instance to indicate the cause of the error: related to eval(). One thing to note here is that it is not supported by the current ECMAScript specification and will not be thrown by the runtime. Instead, we can use the

SyntaxError

error. However, it remains backwards compatible with earlier versions of ECMAScript.

Grammar

new EvalError([message[, fileName[, lineNumber]]])

Example

try{
  throw new EvalError('Eval Error Occurred');
} 
catch(e){
  console.log(e instanceof EvalError); // true
  console.log(e.message);    // "Eval Error Occurred"
  console.log(e.name);       // "EvalError"
  console.log(e.stack);      // "EvalError: Eval Error Occurred..."
}

Browser Compatibility

2. RangeError

Create an

error

Instance, indicating the cause of the error: the numerical variable or parameter exceeds its valid range. <p><span type="button" class="copyCode code-tool" data-toggle="tooltip" data-placement="top" data-clipboard-text="new RangeError([message[, fileName[, lineNumber]]]) " title="" data-original-title="复制"></span></p><pre class="brush:js;toolbar:false;">new RangeError([message[, fileName[, lineNumber]]])</pre><p>下面的情况会触发该错误：</p> <p>1）根据<code>String.prototype.normalize()，我们传递了一个不允许的字符串值。

// Uncaught RangeError: The normalization form should be one of NFC, NFD, NFKC, NFKD
String.prototype.normalize(“-1”)

2）使用Array构造函数创建非法长度的数组

// RangeError: Invalid array length
var arr = new Array(-1);

3）诸如 Number.prototype.toExponential()，Number.prototype.toFixed()或Number.prototype.toPrecision()之类的数字方法会接收无效值。

// Uncaught RangeError: toExponential() argument must be between 0 and 100
Number.prototype.toExponential(101)
// Uncaught RangeError: toFixed() digits argument must be between 0 and 100
Number.prototype.toFixed(-1)
// Uncaught RangeError: toPrecision() argument must be between 1 and 100
Number.prototype.toPrecision(101)

事例

对于数值

function checkRange(n)
{
    if( !(n >= 0 && n <= 100) )
    {
        throw new RangeError("The argument must be between 0 and 100.");
    }
};
try
{
    checkRange(101);
}
catch(error)
{
    if (error instanceof RangeError)
    {
        console.log(error.name);
        console.log(error.message);
    }
}

对于非数值

function checkJusticeLeaque(value)
{
    if(["batman", "superman", "flash"].includes(value) === false)
    {
        throw new RangeError('The hero must be in Justice Leaque...');
    }
}
try
{
    checkJusticeLeaque("wolverine");
}
catch(error)
{
    if(error instanceof RangeError)
    {
        console.log(error.name);
        console.log(error.message);
    }
}

浏览器兼容性

3. ReferenceError

创建一个error实例，表示错误的原因：无效引用。

new ReferenceError([message[, fileName[, lineNumber]]])

事例

ReferenceError被自动触发。

try {
  callJusticeLeaque();
} 
catch(e){
  console.log(e instanceof ReferenceError)  // true
  console.log(e.message)        // callJusticeLeaque is not defined
  console.log(e.name)           // "ReferenceError"
  console.log(e.stack)          // ReferenceError: callJusticeLeaque is not defined..
}
or as simple as 
a/10;

显式抛出ReferenceError

try {
  throw new ReferenceError('Reference Error Occurred')
} 
catch(e){
  console.log(e instanceof ReferenceError)  // true
  console.log(e.message) // Reference Error Occurred
  console.log(e.name)   // "ReferenceError"
  console.log(e.stack)  // ReferenceError: Reference Error Occurred.
}

浏览器兼容性

4. SyntaxError

创建一个error实例，表示错误的原因：eval()在解析代码的过程中发生的语法错误。

换句话说，当 JS 引擎在解析代码时遇到不符合语言语法的令牌或令牌顺序时，将抛出SyntaxError。

捕获语法错误

try {
  eval('Justice Leaque');  
} 
catch(e){
  console.error(e instanceof SyntaxError);  // true
  console.error(e.message);    //  Unexpected identifier
  console.error(e.name);       // SyntaxError
  console.error(e.stack);      // SyntaxError: Unexpected identifier
}

let a = 100/; // Uncaught SyntaxError: Unexpected token ';'
// Uncaught SyntaxError: Unexpected token ] in JSON
JSON.parse('[1, 2, 3, 4,]'); 
// Uncaught SyntaxError: Unexpected token } in JSON
JSON.parse('{"aa": 11,}');

创建一个SyntaxError

try {
  throw new SyntaxError('Syntax Error Occurred');
} 
catch(e){
  console.error(e instanceof SyntaxError); // true
  console.error(e.message);    // Syntax Error Occurred
  console.error(e.name);       // SyntaxError
  console.error(e.stack);      // SyntaxError: Syntax Error Occurred
}

浏览器兼容性

5. TypeError

创建一个error实例，表示错误的原因：变量或参数不属于有效类型。

new TypeError([message[, fileName[, lineNumber]]])

下面情况会引发 TypeError：

• 在传递和预期的函数的参数或操作数之间存在类型不兼容。
• 试图更新无法更改的值。
• 值使用不当。

例如：

const a = 10;
a = "string"; // Uncaught TypeError: Assignment to constant variable

null.name // Uncaught TypeError: Cannot read property 'name' of null

捕获TypeError

try {
  var num = 1;
  num.toUpperCase();
} 
catch(e){
  console.log(e instanceof TypeError)  // true
  console.log(e.message)   // num.toUpperCase is not a function
  console.log(e.name)      // "TypeError"
  console.log(e.stack)     // TypeError: num.toUpperCase is not a function
}

创建 TypeError

try {
  throw new TypeError('TypeError Occurred') 
} 
catch(e){
  console.log(e instanceof TypeError)  // true
  console.log(e.message)          // TypeError Occurred
  console.log(e.name)             // TypeError
  console.log(e.stack)            // TypeError: TypeError Occurred
}

浏览器兼容性

6. URIError

创建一个error实例，表示错误的原因：给 encodeURI()或  decodeURl()传递的参数无效。

如果未正确使用全局URI处理功能，则会发生这种情况。

简单来说，当我们将不正确的参数传递给encodeURIComponent()或decodeURIComponent()函数时，就会引发这种情况。

new URIError([message[, fileName[, lineNumber]]])

encodeURIComponent()通过用表示字符的UTF-8编码的一个，两个，三个或四个转义序列替换某些字符的每个实例来对URI进行编码。

// "https%3A%2F%2Fmedium.com%2F"
encodeURIComponent('https://medium.com/');

decodeURIComponent()——对之前由encodeURIComponent创建的统一资源标识符(Uniform Resource Identifier, URI)组件进行解码。

// https://medium.com/
decodeURIComponent("https%3A%2F%2Fmedium.com%2F")

捕捉URIError

try {
  decodeURIComponent('%')
} 
catch (e) {
  console.log(e instanceof URIError)  // true
  console.log(e.message)              // URI malformed
  console.log(e.name)                 // URIError
  console.log(e.stack)                // URIError: URI malformed...
}

显式抛出URIError

try {
  throw new URIError('URIError Occurred')
} 
catch (e) {
  console.log(e instanceof URIError)  // true
  console.log(e.message)        // URIError Occurred
  console.log(e.name)           // "URIError"
  console.log(e.stack)          // URIError: URIError Occurred....
}

浏览器兼容性

英文原文地址：http://help.dottoro.com/ljfhismo.php

作者：Isha Jauhari

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