no-mixed-requires.md

node/no-mixed-requires

disallow require calls to be mixed with regular variable declarations

In the Node.js community it is often customary to separate initializations with calls to require modules from other variable declarations, sometimes also grouping them by the type of module. This rule helps you enforce this convention.

📖 Rule Details

When this rule is enabled, each var statement must satisfy the following conditions:

• either none or all variable declarations must be require declarations (default)
• all require declarations must be of the same type (grouping)

This rule distinguishes between six kinds of variable declaration types:

• core: declaration of a required [core module][1]
• file: declaration of a required [file module][2]
• module: declaration of a required module from the [node_modules folder][3]
• computed: declaration of a required module whose type could not be determined (either because it is computed or because require was called without an argument)
• uninitialized: a declaration that is not initialized
• other: any other kind of declaration

In this document, the first four types are summed up under the term require declaration.

var fs = require('fs'),        // "core"     \
    async = require('async'),  // "module"   |- these are "require declaration"s
    foo = require('./foo'),    // "file"     |
    bar = require(getName()),  // "computed" /
    baz = 42,                  // "other"
    bam;                       // "uninitialized"

Options

This rule can have an object literal option whose two properties have false values by default.

Configuring this rule with one boolean option true is deprecated.

Examples of incorrect code for this rule with the default { "grouping": false, "allowCall": false } options:

/*eslint node/no-mixed-requires: "error"*/

var fs = require('fs'),
    i = 0;

var async = require('async'),
    debug = require('diagnostics').someFunction('my-module'),
    eslint = require('eslint');

Examples of correct code for this rule with the default { "grouping": false, "allowCall": false } options:

/*eslint node/no-mixed-requires: "error"*/

// only require declarations (grouping off)
var eventEmitter = require('events').EventEmitter,
    myUtils = require('./utils'),
    util = require('util'),
    bar = require(getBarModuleName());

// only non-require declarations
var foo = 42,
    bar = 'baz';

// always valid regardless of grouping because all declarations are of the same type
var foo = require('foo' + VERSION),
    bar = require(getBarModuleName()),
    baz = require();

grouping

Examples of incorrect code for this rule with the { "grouping": true } option:

/*eslint node/no-mixed-requires: ["error", { "grouping": true }]*/

// invalid because of mixed types "core" and "module"
var fs = require('fs'),
    async = require('async');

// invalid because of mixed types "file" and "unknown"
var foo = require('foo'),
    bar = require(getBarModuleName());

allowCall

Examples of incorrect code for this rule with the { "allowCall": true } option:

/*eslint node/no-mixed-requires: ["error", { "allowCall": true }]*/

var async = require('async'),
    debug = require('diagnostics').someFunction('my-module'), /* allowCall doesn't allow calling any function */
    eslint = require('eslint');

Examples of correct code for this rule with the { "allowCall": true } option:

/*eslint node/no-mixed-requires: ["error", { "allowCall": true }]*/

var async = require('async'),
    debug = require('diagnostics')('my-module'),
    eslint = require('eslint');

Known Limitations

• The implementation is not aware of any local functions with the name require that may shadow Node.js' global require.

• Internally, the list of core modules is retrieved via require("repl")._builtinLibs. If you use different versions of Node.js for ESLint and your application, the list of core modules for each version may be different. The above mentioned _builtinLibs property became available in 0.8, for earlier versions a hardcoded list of module names is used as a fallback. If your version of Node.js is older than 0.6 that list may be inaccurate.

🔎 Implementation

• Rule source
• Test source