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Array. The from method

The array. from method is used to convert two types of objects into real arrays:

  • Array-like object (array-like object)

    let arrayLike = {
    '0': 'a',
    '1': 'b',
    '2': 'c',
    length: 3
};
let arr = Array.from(arrayLike); // ['a', 'b', 'c']
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The so-called array-like object has only one essential feature, that is, it must have the length attribute. Therefore, any object with a length attribute can be converted to an Array using the array. from method.

  • Iterable objects (including sets and maps)

    Array.from('hello') // ['h', 'e', 'l', 'l', 'o'] let namesSet = new Set(['a', 'b']) Array.from(namesSet) // ['a', 'b'] // Both strings and Set structures have Iterator interfaces, so array. from can be converted to true arrays.Copy the code

An Array of method

The array.of () method converts a set of values to an Array.

Array.of(1, 2, 3)
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Print result:

Flat method

Used to “flatten” a nested array into a one-dimensional array. Returns a new array, with no effect on the original data.

[1, 2, [3, 4]].flat()
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Flat () only “flattens” one layer by default.

If you want to “flatten” a multi-tier nested array, you can write the argument to the flat() method as an integer.

[1, 2, [3, [4, 5]]].flat(2)
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If you’re not sure how many layers there are, but you want to convert them to a one-dimensional array, you can pass the keyword Infinity

[1, 2, [3, [4, [5,6]]]]. Flat (Infinity)Copy the code

The fill method

Given a value, populate the array.

Arr. fill(value, start, end) -value: indicates the fill value. - start: indicates the start position, which can be omitted. - end: indicates the end position, which can be omitted. The actual end position is end-1.Copy the code

Suppose you already have an array and want to replace all of its values with the specified values

You can also replace data at a specified location (or within a specified location range)

CopyWithin method

Inside the current array, copies the member at the specified location to another location (overwriting the original member), and returns the current array. Modifies the current array.

Arr. CopyWithin (target, start, end) - target (required) : Replace data from this location. - start (Optional) : indicates the start location of the replication source. The default value is 0. If it is negative, it is the reciprocal. - end (Optional) : indicates the end position of the replication source. The default value is the array length. If it is negative, it is the reciprocal. The actual end position is end-1.Copy the code

Take a look at some examples:

So here we’re going to copy the elements at subscript 3-5 and overwrite them from subscript 1.

Both start and end are optional. If left blank, the entire array is copied, and if there are not enough target positions, as many as can be overwritten.

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Phase to recommend

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👉 15 JavaScript array practical tips

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