Node.js – process.emitWarning() Method

The process.emitWarning() method can be used to emit custom or user-defined process warnings. This can be listened by adding a handler to the warning event.

Syntax

process.emitWarning(warning, [options])

Parameters

• warning – This is the warning that will be emitted.

• options –

  • type – This is the type of warning being emitted. Default ‘Warning’

  • code – This is a unique identifier for the warning that will be emitted.

  • ctor – This is an optional function used to limit the generated stack trace.

  • detail – This is the additional text to be included with the error.

Example 1

Create a file with the name "warning.js" and copy the following code snippet. After creating the file, use the command "node warning.js" to run this code.

console.log("Start ...");

// Interval set to keep the process running
setInterval(() => {
console.log("Running ...");}, 1000);

setTimeout(() => {
   process.emitWarning('An Error occured!', {
      code: 'Custom_Warning',
      detail: 'Additional information about warning'
   });
}, 4000);

// Start listening
process.on('warning', (warning) => {

   // Print msg if there is a warning
   if (warning) {
      console.log(warning);
      process.exit(0);
   }
});

Output

Start ...
Running ...
Running ...
Running ...
{ [object Object]: An Error occured!
at Timeout.setTimeout (/home/cg/root/8008764/main.js:8:12)
at ontimeout (timers.js:386:14)
at tryOnTimeout (timers.js:250:5)
at Timer.listOnTimeout (timers.js:214:5)
name:
{ code: 'Custom_Warning',
detail: 'Additional information about warning' } }
(node:13011) [object Object]: An Error occured!

Example 2

Let’s take a look at one more example.

console.log("Start ...");

// Interval set to keep the process running
setInterval(() => {
   console.log("Running ...");
}, 1000);

setTimeout(() => {
   process.emitWarning('An Error occured!', {
      code: 'Custom_Warning',
      detail: 'Additional information about warning'
   });
}, 2000);

setTimeout(() => {
   process.emitWarning('ALERT! WARNING OCCURED', {
      type: 'IMPORTANT',
      code: '001',
      detail: 'Can not proceed further!'
   });
}, 4000);

// Start listening
process.on('warning', (warning) => {

   // Print msg if there is an Important warning
   if (warning.name === 'IMPORTANT') {
      console.log('Fix this ASAP!')
      process.exit(0);
   }
});

Output

Start ...
Running ...
Running ...
Running ...
Running ...
Running ...
Running ...
Running ...
Running ...
Running ...
(node:18756) [object Object]: An Error occured!
(node:18756) [object Object]: ALERT! WARNING OCCURED