156 lines
2.7 KiB
Markdown
156 lines
2.7 KiB
Markdown
---
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title: Error Handling and Try Catch Throw
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localeTitle: 错误处理和尝试抓住投掷
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---
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## 错误处理和尝试抓住投掷
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`try...catch..finally`语句标记要尝试的语句块，并指定响应，如果抛出异常。 `try`语句包含一个或多个语句，以及至少一个`catch`子句或`finally`子句，或两者。
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#### `try...catch` ：
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```javascript
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try {
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throw new Error('my error');
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}
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catch (e) {
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console.error(e.message);
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}
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// Output:
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// my error
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```
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#### `try...finally` ：
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```javascript
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try {
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throw new Error('my error');
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}
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finally {
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console.error('finally');
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}
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// Output:
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// finally
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```
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_注意：_当你没有`catch`到错误时，它实际上并没有被“ `catch` ”，即使执行了`finally`块。这意味着错误将继续到上面的`try`块（或主块）。
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#### `try...catch...finally` ：
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```javascript
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try {
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throw new Error('my error');
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}
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catch (e) {
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console.error(e.message);
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}
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finally {
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console.error('finally');
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}
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// Output:
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// my error
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// finally
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```
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典型用法：
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```javascript
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try {
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openFile(file);
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readFile(file)
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}
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catch (e) {
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console.error(e.message);
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}
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finally {
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closeFile(file);
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}
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```
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#### 嵌套`try...catch` ：
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你也可以：
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* 在`try`块中嵌入`try-catch`语句。
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* 向上抛出错误。
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```javascript
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try {
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try {
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throw new Error('my error');
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}
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catch (e) {
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console.error('inner', e.message);
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throw e;
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}
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finally {
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console.log('finally');
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}
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}
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catch (e) {
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console.error('outer', e.message);
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}
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// Output:
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// inner my error
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// finally
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// outer my error
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```
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#### 错误类型
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##### 参考错误
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```javascript
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var x;
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try {
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x = y + 1; // y cannot be referenced (used)
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}
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catch(err) {
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console.log(err.name, err.message);
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}
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// ReferenceError y is not defined
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```
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##### 语法错误
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```javascript
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try {
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eval("alert('Hello)"); // Missing ' will produce an error
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}
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catch(err) {
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console.log(err.name,err.message);
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}
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// SyntaxError Invalid or unexpected token
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```
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##### 输入错误
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```javascript
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var num = 1;
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try {
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num.toUpperCase(); // You cannot convert a number to upper case
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}
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catch(err) {
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console.log(err.name, err.message);
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}
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// TypeError num.toUpperCase is not a function
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```
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##### URI错误
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```javascript
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try {
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decodeURI("%%%"); // You cannot URI decode these percent signs
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}
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catch(err) {
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console.log(err.name, err.message);
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}
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// URIError URI malformed
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```
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#### 更多信息：
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[MDN](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/try…catch) [W3S](https://www.w3schools.com/js/js_errors.asp) |