JS uses a try catch to catch an exception

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Introduction to the

The front end is at the forefront of customer penetration, with special attention to user experience. During development, the occurrence of exceptions cannot be controlled due to various problems. Therefore, exceptions need to be handled to optimize user experience.

Try catch finally

The **try** statement allows you to define a block of code for error testing at execution time.

The catch statement allows you to define which block of code to execute when an error occurs with the try block.

Finally statements are executed after a try and catch with or without exceptions.

Note: Both catch and finally statements are optional, but at least one must be used when using a try statement. When an error occurs, JavaScript stops execution and generates an error message. You can use the throw statement to create a custom message (throwing an exception)

try {
    // tryCode - Try to execute a block of code
}
catch(err) {
    // catchCode - catch the error code block
}
finally {
    // finallyCode - a block of code that executes regardless of the result of the try/catch
}
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The need for exception handling

Enhanced user experience, accurate problem location, and improved front-end solutions, such as front-end monitoring systems

Exception handling scenarios

JS syntax error, code exception

Abnormal Promise

The Iframe abnormal

Cross-domain abnormal

The interface failed to request an AJAX request. Procedure

The static resource import fails to be loaded

Try catch

Only synchronous exceptions can be caught, but syntax and asynchronous exceptions cannot be caught. Therefore, you need to pay attention to them in daily use

// Failed to catch syntax exceptions
try { 
  let name = 'aaa // write less '
  } catch(e) {
  console.log('Exception caught:',e); 
}
// VM421:1 Uncaught SyntaxError: Unexpected identifier

// Cannot catch asynchronous exceptions
try { 
  setTimeout(() = > { 
    console.log(a) // The variable a is not declared
  }, 1000)}catch(e) { 
  console.log('Exception caught:',e); 
} 
// blog.js:1 Uncaught ReferenceError: a is not defined
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JS uses a try catch to catch an exception