Array The from method creates an undefined array of length n

// Create a 12 individual undefined Array of components 

Array.from({length:12})

 Equivalent to 

[...Array(12)]

Some extensions use  

Array.from({length:12}).forEach((v,i,ar) => {
console.log(v,i)
});

Usually we can quickly create an array of natural numbers , for example

Array.from({length:12}).forEach((v,i,ar) => {
console.log(i+1+' month ');
//console.log(' The first '+(i+1)+' quarter ');
//console.log(' The first '+(i+1)+' school year ');
});

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Quickly create the alphabet 、 Natural number array

[...Array(10)].map((v,i) => 0)//0, 0, 0, 0, 0, 0, 0, 0, 0, 0

[...Array(10)].map((v,i) => i)//0, 1, 2, 3, 4, 5, 6, 7, 8, 9

[...Array(26)].map((v,i) => String.fromCharCode(i + 65))// Output alphabet