JavaScript Arrays Best Practices

1. Use the literal syntax for array creation.
// bad const items = new Array(); // good const items = [];
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');
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. To convert an iterable object to an array, use spreads ... instead of Array.from.
const foo = document.querySelectorAll('.foo'); // good const nodes = Array.from(foo); // best const nodes = [...foo];
5. Use Array.from for converting an array-like object to an array.
const arrLike = { 0: 'foo', 1: 'bar', 2: 'baz', length: 3 }; // bad const arr = Array.prototype.slice.call(arrLike); // good const arr = Array.from(arrLike);
6. Use Array.from instead of spread ... for mapping over iterables, because it avoids creating an intermediate array.
// bad const baz = [...foo].map(bar); // good const baz = Array.from(foo, bar);
7. 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, ];

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