No Iterators

Don't use iterators. Prefer JavaScript's higher-order functions instead of loops like for-in or for-of. Dealing with pure functions that return values is easier to reason about than side effects and enforces the immutable rule of this style guide.

Use

• map()
• every()
• filter()
• find()
• findIndex()
• reduce()
• some()
• ...

to iterate over arrays, and

• Object.keys()
• Object.values()
• Object.entries()

to produce arrays to iterate over objects.

ESLint: no-iterator and no-restricted-syntax

Examples

⇣ Incorrect code for this rule:

const snowflakes = [1, 2, 3, 4, 5];

let flakes = 0;
for (let flake of snowflakes) {
  flakes += flake;
}
flakes === 15;

const snowflakes = [1, 2, 3, 4, 5];

const increasedByOne = [];
for (let i = 0; i < snowflakes.length; i++) {
  increasedByOne.push(snowflakes[i] + 1);
}

⇡ Correct code for this rule:

const snowflakes = [1, 2, 3, 4, 5];

let flakes = 0;
snowflakes.forEach(flake => {
  flakes += flake;
});
flakes === 15;

const snowflakes = [1, 2, 3, 4, 5];

const increasedByOne = [];
snowflakes.forEach(flake => {
  increasedByOne.push(flake + 1);
});

⇢ Recommended code for this rule:

const snowflakes = [1, 2, 3, 4, 5];

const flakes = snowflakes.reduce((total, flake) => total + flake, 0);
flakes === 15;

const snowflakes = [1, 2, 3, 4, 5];

const increasedByOne = snowflakes.map(flake => flake + 1);

No Generators

Don't use generators for now since they don't transpile well to ES5.

Spacing

If the usage of generators is necessary, or disregard the rule to not use generators, make sure their function signature is spaced properly. The function and * syntax are part of the same conceptual keyword - * is not a modifier for function, function* is a unique construct, different from function.

Examples

↯ Critical incorrect code for this rule:

function
*
snow() {
  // ...
}

const snow = function
*
() {
  // ...
};

⇣ Incorrect code for this rule:

function * snow() {}

const snow = function * () {}

const snow = function *() {}

const snow = function*() {}

function*snow() {}

function *snow() {}

⇡ Correct code for this rule:

function* snow() {}

const snow = function*() {};