@putout/plugin-for-of

@putout/plugin-for-of

The for...of statement creates a loop which invokes a custom iteration hook with statements to be executed for the value of each element of an array.

(c) MDN

🐊Putout plugin adds support of transformation for...of statements.

Install

npm i @putout/plugin-for-of

Rules

• ✅ add-missing-declaration;
• ✅ for-each;
• ✅ for-entries;
• ✅ for-entries-n;
• ✅ for-in-negative;
• ✅ for-in-positive;
• ✅ for-length;
• ✅ for-n;
• ✅ map;
• ✅ reduce;
• ✅ remove-unused-variables;
• ✅ remove-useless;
• ✅ remove-useless-array-from;
• ✅ remove-useless-variables;
• ✅ to-for-n;

Configuration

{
    "rules": {
        "for-of/add-missing-declaration": "on",
        "for-of/map": "on",
        "for-of/for-in": "on",
        "for-of/for-each": "on",
        "for-of/reduce": "on",
        "for-of/remove-unused-variables": "on",
        "for-of/remove-useless": "on",
        "for-of/remove-useless-array-from": "on",
        "for-of/remove-useless-variables": ["on", {
            "maxProperties": 4
        }],
        "for-of/for": "on",
        "for-of/to-for-n": "on"
    }
}

add-missing-declaration

The const declaration declares block-scoped local variables.

(c) MDN

Checkout in 🐊Putout Editor.

❌ Example of incorrect code

for (name of names) {
    alert(`hello ${name}`);
}

✅ Example of correct code

for (const name of names) {
    alert(`hello ${name}`);
}

map

The map() method creates a new array populated with the results of calling a provided function on every element in the calling array.

(c) MDN

❌ Example of incorrect code

names.map((name) => {
    alert(`hello ${name}`);
});

✅ Example of correct code

for (const name of names) {
    alert(`hello ${name}`);
}

for-in

The for...in statement iterates over all enumerable properties of an object that are keyed by strings.

(c) MDN

❌ Example of incorrect code

for (const item in object) {
    if (object.hasOwnProperty(item))
        log(item);
}

for (const item in object) {
    if (!object.hasOwnProperty(item))
        continue;
    
    log(item);
}

✅ Example of correct code

for (const item of Object.keys(object)) {
    log(item);
}

for-each

The forEach() method executes a provided function once for each array element.

(c) MDN

❌ Example of incorrect code

Object
    .keys(json)
    .forEach((name) => {
        manage(name, json[name]);
    });

[].forEach.call(arguments, (item) => {
    console.log(item);
});

✅ Example of correct code

for (const name of Object.keys(json)) {
    manage(name, json[name]);
}

for (const item of arguments) {
    console.log(item);
}

reduce

• The reduce() method executes a user-supplied reducer callback function on each element of the array, in order, passing in the return value from the calculation on the preceding element. The final result of running the reducer across all elements of the array is a single value.

(c) MDN

You should always look at second argument of a reducer since it changes logic drastically and should read back and forth a couple times to understand what is going on.

Recursive functions like .reduce() can be powerful but sometimes difficult to understand, especially for less experienced JavaScript developers. If code becomes clearer when using other array methods, developers must weigh the readability tradeoff against the other benefits of using .reduce(). In cases where .reduce() is the best choice, documentation and semantic variable naming can help mitigate readability drawbacks.

(c) MDN

Check it out in 🐊Putout Editor.

❌ Example of incorrect code

const result = list.reduce((a, b) => a + b, 1);

✅ Example of correct code

let sum = 1;

for (const a of list) {
    sum += a;
}

remove-unused-variables

❌ Example of incorrect code

for (const {a, b} of c) {
    console.log(a);
}

✅ Example of correct code

for (const {a} of c) {
    console.log(a);
}

remove-useless

The Array enables storing a collection of multiple items under a single variable name.

(c) MDN

❌ Example of incorrect code

for (const a of ['hello']) {
    console.log(a);
}

✅ Example of correct code

console.log('hello');

remove-useless-variables

❌ Example of incorrect code

for (const a of b) {
    const {c} = a;
}

✅ Example of correct code

for (const {c} of b) {}

remove-useless-array-from

The Array.from() static method creates a new, shallow-copied Array instance from an iterable or array-like object.

(c) MDN

❌ Example of incorrect code

for (const x of Array.from(y)) {}

✅ Example of correct code

for (const x of y) {}

for

The for statement creates a loop that consists of three optional expressions, enclosed in parentheses and separated by semicolons, followed by a statement to be executed in the loop.

(c) MDN

for-n

❌ Example of incorrect code

const n = items.length;

for (let i = 0; i < n; i++) {
    const item = items[i];
    log(item);
}

✅ Example of correct code

for (const item of items) {
    log(item);
}

for-length

❌ Example of incorrect code

for (let i = 0; i < array.length; i++) {
    const item = array[i];
    console.log(item);
}

✅ Example of correct code

for (const item of items) {
    log(item);
}

for-entries

❌ Example of incorrect code

for (let i = 0; i < array.length; i++) {
    const item = array[i];
    console.log(i, item);
}

✅ Example of correct code

for (const [i, item] of array.entries()) {
    console.log(i, item);
}

for-entries-n

❌ Example of incorrect code

const n = array.length;

for (let i = 0; i < n; i++) {
    const item = array[i];
    console.log(i, item);
}

✅ Example of correct code

for (const [i, item] of array.entries()) {
    console.log(i, item);
}

to-for-n

The entries() method of Array instances returns a new array iterator object that contains the key/value pairs for each index in the array.

(c) MDN

Index overwrites on each iteration so when it modified inside loop it has no effect so for should be used in this case. Checkout in 🐊Putout Editor.

❌ Example of incorrect code

for (let [i, token] of tokens.entries()) {
    ++i;
}

✅ Example of correct code

const n = tokens.length;

for (let i = 0; i < n; i++) {
    ++i;
}

License

MIT