prefer-destructuring

Require destructuring from arrays and/or objects

With JavaScript ES6, a new syntax was added for creating variables from an array index or object property, called destructuring. This rule enforces usage of destructuring instead of accessing a property through a member expression.

Rule Details

Options

This rule takes two arguments, both of which are objects. The first object parameter determines what types of destructuring the rule applies to.

In the first object, there are two properties, array and object, that can be used to turn on or off the destructuring requirement for each of those types independently. By default, both are true.

{
  "rules": {
    "prefer-destructuring": ["error", {
      "array": true,
      "object": true
    }]
  }
}
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For example, the following configuration enforces only object destructuring, but not array destructuring:

{
  "rules": {
    "prefer-destructuring": ["error", {"object": true, "array": false}]
  }
}
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Examples of incorrect code for this rule:

/* eslint prefer-destructuring: "error" */

// With `array` enabled
var foo = array[0];
bar.baz = array[0];

// With `object` enabled
var foo = object.foo;
var foo = object['foo'];
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Examples of correct code for this rule:

/* eslint prefer-destructuring: "error" */

// With `array` enabled
var [ foo ] = array;
var foo = array[someIndex];
[bar.baz] = array;


// With `object` enabled
var { foo } = object;

var foo = object.bar;

let bar;
({ bar } = object);
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Alternatively, you can use separate configurations for different assignment types. The first argument accepts two other keys instead of array and object.

One key is VariableDeclarator and the other is AssignmentExpression, which can be used to control the destructuring requirement for each of those types independently. Each property is an object containing two properties, array and object, which can be used to control the destructuring requirement for each of array and object independently for variable declarations and assignment expressions. By default, array and object are set to true for both VariableDeclarator and AssignmentExpression.

{
  "rules": {
    "prefer-destructuring": ["error", {
      "VariableDeclarator": {
        "array": true,
        "object": true
      },
      "AssignmentExpression": {
        "array": true,
        "object": true
      }
    }]
  }
}
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Examples of correct code when object destructuring in VariableDeclarator is enforced:

/* eslint prefer-destructuring: ["error", {VariableDeclarator: {object: true}}] */
var {bar: foo} = object;
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Examples of correct code when array destructuring in AssignmentExpression is enforced:

/* eslint prefer-destructuring: ["error", {AssignmentExpression: {array: true}}] */
[bar] = array;
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enforceForRenamedProperties

The rule has a second object argument with a single key, enforceForRenamedProperties, which determines whether the object destructuring applies to renamed variables.

{
  "rules": {
    "prefer-destructuring": ["error",
    {
      "object": true
    },
    {
      "enforceForRenamedProperties": true
    }]
  }
}
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Examples of incorrect code when enforceForRenamedProperties is enabled:

/* eslint "prefer-destructuring": ["error", { "object": true }, { "enforceForRenamedProperties": true }] */
var foo = object.bar;
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Examples of correct code when enforceForRenamedProperties is enabled:

/* eslint "prefer-destructuring": ["error", { "object": true }, { "enforceForRenamedProperties": true }] */
var { bar: foo } = object;
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Examples of additional correct code when enforceForRenamedProperties is enabled:

/* eslint "prefer-destructuring": ["error", { "object": true }, { "enforceForRenamedProperties": true }] */
class C {
    #x;
    foo() {
        const bar = this.#x; // private identifiers are not allowed in destructuring
    }
}
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Note: It is not possible to determine if a variable will be referring to an object or an array at runtime. This rule therefore guesses the assignment type by checking whether the key being accessed is an integer. This can lead to the following possibly confusing situations:

• Accessing an object property whose key is an integer will fall under the category array destructuring.
• Accessing an array element through a computed index will fall under the category object destructuring.

The --fix option on the command line fixes only problems reported in variable declarations, and among them only those that fall under the category object destructuring. Furthermore, the name of the declared variable has to be the same as the name used for non-computed member access in the initializer. For example, var foo = object.foo can be automatically fixed by this rule. Problems that involve computed member access (e.g., var foo = object[foo]) or renamed properties (e.g., var foo = object.bar) are not automatically fixed.

When Not To Use It

If you want to be able to access array indices or object properties directly, you can either configure the rule to your tastes or disable the rule entirely.

Additionally, if you intend to access large array indices directly, like:

var foo = array[100];
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Then the array part of this rule is not recommended, as destructuring does not match this use case very well.

Or for non-iterable ‘array-like’ objects:

var $ = require('jquery');
var foo = $('body')[0];
var [bar] = $('body'); // fails with a TypeError
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Version

This rule was introduced in ESLint v3.13.0.

Further Reading

Destructuring assignment - JavaScript | MDN
developer.mozilla.org

Destructuring and parameter handling in ECMAScript 6
2ality.com

Resources

• Rule source
• Tests source