4.1 Use the literal syntax for array creation. eslint: no-array-constructor
// bad
const items = new Array();
// good
const items = [];
4.2 Use Array#push instead of direct assignment to add items to an array.
const someStack = [];
// bad
someStack[someStack.length] = 'abracadabra';
// good
someStack.push('abracadabra');
4.3 Use array spreads ... to copy arrays.
// bad
const len = items.length;
const itemsCopy = [];
let i;
for (i = 0; i < len; i += 1) {
itemsCopy[i] = items[i];
}
// good
const itemsCopy = [...items];
4.4 To convert an array-like object to an array, use Array.from.
const foo = document.querySelectorAll('.foo');
const nodes = Array.from(foo);
4.5 Use return statements in array method callbacks. It’s ok to omit the return if the function body consists of a single statement returning an expression without side effects, following 8.2. eslint: array-callback-return
// good
[1, 2, 3].map((x) => {
const y = x + 1;
return x * y;
});
// good
[1, 2, 3].map(x => x + 1);
// bad
const flat = {};
[[0, 1], [2, 3], [4, 5]].reduce((memo, item, index) => {
const flatten = memo.concat(item);
flat[index] = flatten;
});
// good
const flat = {};
[[0, 1], [2, 3], [4, 5]].reduce((memo, item, index) => {
const flatten = memo.concat(item);
flat[index] = flatten;
return flatten;
});
// bad
inbox.filter((msg) => {
const { subject, author } = msg;
if (subject === 'Mockingbird') {
return author === 'Harper Lee';
} else {
return false;
}
});
// good
inbox.filter((msg) => {
const { subject, author } = msg;
if (subject === 'Mockingbird') {
return author === 'Harper Lee';
}
return false;
});
4.6 Use line breaks after open and before close array brackets if an array has multiple lines
// bad
const arr = [
[0, 1], [2, 3], [4, 5],
];
const objectInArray = [{
id: 1,
}, {
id: 2,
}];
const numberInArray = [
1, 2,
];
// good
const arr = [[0, 1], [2, 3], [4, 5]];
const objectInArray = [
{
id: 1,
},
{
id: 2,
},
];
const numberInArray = [
1,
2,
];