prefer-spread.md

Prefer the spread operator over Array.from(…), Array#concat(…), Array#{slice,toSpliced}() and String#split('')

💼 This rule is enabled in the ✅ recommended config.

🔧💡 This rule is automatically fixable by the --fix CLI option and manually fixable by editor suggestions.

Enforces the use of the spread operator (...) over outdated patterns. This also helps keep consistency by using a single flexible operator instead of:

• Array.from(…)

  Convert Iterable to Array.

  This rule adds on to the built-in prefer-spread rule, which only flags uses of .apply(). Does not enforce for TypedArray.from().

• Array#concat(…)

  Concat an Array with one or more Array's or Array elements.

• Array#slice()

  Shallow copy an Array.

  Variables named arrayBuffer, blob, buffer, file, and this are ignored.

• Array#toSpliced()

  Shallow copy an Array.

• String#split('')

  Split a string into an array of characters.

  Note: The suggestion fix may get different result.

To enforce the spread operator over Object#assign(), use the built-in prefer-object-spread rule.

Fail

Array.from(set).map(element => foo(element));

const array = array1.concat(array2);

const copy = array.slice();

const copy = array.slice(0);

const copy = array.toSpliced();

const characters = string.split('');

Pass

[...set].map(element => foo(element));

const array = [...array1, ...array2];

const tail = array.slice(1);

const copy = [...array];

const characters = [...string];

With the unicorn/no-useless-spread rule

Some cases are fixed using extra spread syntax. Therefore we recommend enabling the unicorn/no-useless-spread rule to fix it.

For example:

const baz = [2];
call(foo, ...[bar].concat(baz));

Will be fixed to:

const baz = [2];
call(foo, ...[bar, ...baz]);

unicorn/no-useless-spread will fix it to:

const baz = [2];
call(foo, bar, ...baz);