How to use flatMap function

array.flatmap() is a built-in function in javascript that flattens input array elements into a new array. This method first maps each element using a mapping function and then flattens the input array elements into a new array. Let's take a look at the specific usage of flatMap().

The basic syntax of flatMap() is:

var A = array.flatMap(function callback(current_value, index, Array))
{
    //返回的新数组元素
}

callback: This is a new array with the help of three parameters A function that generates elements as follows:

current_value: It is the input array element.

index: This is optional. It is the index of the input element.

Array: This is optional. It is used when calling array mapping.

Let’s look at two specific examples

Example 1:

The code is as follows

<script>  
var A = [ 1, 2, 3, 4, 5 ];  
b = A.map(x => [x * 3]); 
document.write(b);  
c = arr1.flatMap(x => [x * 3]); 
document.write(c);  
d = arr1.flatMap(x => [[ x * 3 ]]); 
document.write(d); 
</script>

The output result is:

[[3]，[6]，[9]，[12]，[15]] 
[3,6,9,12,15] 
[[3]，[6]，[9]，[12]，[ 15]

Example 2:

The code is as follows

<script> 
var A = [ 1, 2, 3, 4, 5 ]; 
array.flatMap(x => [x * 3]); 
b = A.reduce((acc, x) => acc.concat([ x * 3 ]), []); 
document.write(b); 
</script>

The output result is: [3,6,9,12,15]

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