Cognitive Complexity

Cognitive Complexity is a measure of how difficult a unit of code is to intuitively understand. Unlike Cyclomatic Complexity, which determines how difficult your code will be to test, Cognitive Complexity tells you how difficult your code will be to read and comprehend.

A method's cognitive complexity is based on a few simple rules:

• Code is not considered more complex when it uses shorthand that the language provides for collapsing multiple statements into one
• Code is considered more complex for each "break in the linear flow of the code"
• Code is considered more complex when "flow breaking structures are nested"

Further reading

• Cognitive Complexity docs
• Cognitive Complexity: A new way of measuring understandability

Disallow process.exit() (no-process-exit)

The process.exit() method in Node.js is used to immediately stop the Node.js process and exit. This is a dangerous operation because it can occur in any method at any point in time, potentially stopping a Node.js application completely when an error occurs. For example:

if (somethingBadHappened) {
    console.error("Something bad happened!");
    process.exit(1);
}

This code could appear in any module and will stop the entire application when somethingBadHappened is truthy. This doesn't give the application any chance to respond to the error. It's usually better to throw an error and allow the application to handle it appropriately:

if (somethingBadHappened) {
    throw new Error("Something bad happened!");
}

By throwing an error in this way, other parts of the application have an opportunity to handle the error rather than stopping the application altogether. If the error bubbles all the way up to the process without being handled, then the process will exit and a non-zero exit code will returned, so the end result is the same.

Rule Details

This rule aims to prevent the use of process.exit() in Node.js JavaScript. As such, it warns whenever process.exit() is found in code.

Examples of incorrect code for this rule:

/*eslint no-process-exit: "error"*/

process.exit(1);
process.exit(0);

Examples of correct code for this rule:

/*eslint no-process-exit: "error"*/

Process.exit();
var exit = process.exit;

When Not To Use It

There may be a part of a Node.js application that is responsible for determining the correct exit code to return upon exiting. In that case, you should turn this rule off to allow proper handling of the exit code. Source: http://eslint.org/docs/rules/

Disallow process.exit() (no-process-exit)

The process.exit() method in Node.js is used to immediately stop the Node.js process and exit. This is a dangerous operation because it can occur in any method at any point in time, potentially stopping a Node.js application completely when an error occurs. For example:

if (somethingBadHappened) {
    console.error("Something bad happened!");
    process.exit(1);
}

This code could appear in any module and will stop the entire application when somethingBadHappened is truthy. This doesn't give the application any chance to respond to the error. It's usually better to throw an error and allow the application to handle it appropriately:

if (somethingBadHappened) {
    throw new Error("Something bad happened!");
}

By throwing an error in this way, other parts of the application have an opportunity to handle the error rather than stopping the application altogether. If the error bubbles all the way up to the process without being handled, then the process will exit and a non-zero exit code will returned, so the end result is the same.

Rule Details

This rule aims to prevent the use of process.exit() in Node.js JavaScript. As such, it warns whenever process.exit() is found in code.

Examples of incorrect code for this rule:

/*eslint no-process-exit: "error"*/

process.exit(1);
process.exit(0);

Examples of correct code for this rule:

/*eslint no-process-exit: "error"*/

Process.exit();
var exit = process.exit;

When Not To Use It

There may be a part of a Node.js application that is responsible for determining the correct exit code to return upon exiting. In that case, you should turn this rule off to allow proper handling of the exit code. Source: http://eslint.org/docs/rules/