JS how to quickly create an array with length n

purpose

1. Quickly create a loop N Array of times
2. When simulating false data , Quick creation length is n False data of
3. …

Method 1

1. Create a The length is 10000, Value is empty Array of

const a = new Array(10000).fill(''); // (10000) ['', '','', '', '' ....................., '']

2. Quickly create the specified content ? Take the index as an example

const a = new Array(10000).fill('').map((val, i) => i); // (10000) [0, 1,2, 3, 4 ....................., 9999]

Method 2

1. Create a The length is 10000, Value is empty Array of

const c = Array.from(new Array(10000), () => ''); // (10000) ['', '','', '', '' ....................., '']

2. Create a The length is 10000, The value is index Array of

// (...cont) => cont  This  cont  Is to integrate all parameters of this function, all parameters, all parameters （ Merge into an array   by  cont ）;
// (...cont) => cont  It can also be written here, here, here  (val, i) => [val, i];
const c = Array.from(new Array(10000), (...cont) => cont[1]); // (10000) [0, 1,2, 3, 4 ....................., 9999]
const c = Array.from(new Array(10000), (val, i) => i); // (10000) [0, 1,2, 3, 4 ....................., 9999]

summary

1. Mode one ： Create array , Fill empty string , then map Loop back the newly processed array .
2. Mode two ： adopt Array Of form Static methods pass two parameters , The first is an array , The second parameter is the callback function for processing various values