JS: Array.prototype.slice (extract)

The “slice” function lets you extract a sub-array from a array.

xArray.slice()

Return a copy of array.

console.log([1, 2, 3].slice());
// [ 1, 2, 3 ]

// original not changed
const xx = [1, 2, 3];
const yy = xx.slice();
console.log((xx === yy) === false);
// true

xArray.slice(start)

Start at index start.

Index can be negative. Means count from right.

// take starting at index 1 to end
console.log([0, 1, 2, 3].slice(1));
// [ 1, 2, 3 ]

// take last 2 items
console.log([0, 1, 2, 3].slice(-2));
// [ 2, 3 ]

xArray.slice(start, end)

End at end but does not include end.

console.log([0, 1, 2, 3, 4, 5, 6].slice(1, 2));
// [ 1 ]

// out of bound end index just get the max index
console.log([0, 1, 2].slice(1, 9));
// [ 1, 2 ]

// slice does not convert sparse array to dense array

console.log(Array(4));
// [ <4 empty items> ]

console.log(Array(4).slice());
// [ <4 empty items> ]

// slice can convert array-like object to array
const xx = { "0": "a", "1": "b", "length": 2 };
const yy = Reflect.apply(Array.prototype.slice, xx, []);

console.log(JSON.stringify(xx) === `{"0":"a","1":"b","length":2}`);
console.log(JSON.stringify(yy) === `["a","b"]`);