no for & 100 Array & Uint8Array & Typed Arrays

no for & 100 Array

padStart

const arr = [...``.padStart(100, ` `)].map((item, i) => item = i+1);

const arr = ``;

const result = [...arr.padStart(100, "x")].map((x, i) => x = i+1);
console.log(`result =`, result);

// Array [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100]

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/padStart

bad

function generate100Array() {
    var arr = new Array(100);
    for(var i = 0; i < 100; i++){
        arr[i]='';
    }
    return arr;
}

var a = generate100Array(),
    b = generate100Array();

console.time('for');
for (var i = 0; i < a.length; i++) {
    a[i] = i;
}
console.timeEnd('for');

console.time('forEach');
b.forEach(function (el, index) {
    b[index] = index;
});
console.timeEnd('forEach');

for is better than forEach

map

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Array 100 & no for

https://www.quora.com/Given-an-array-with-100-elements-numbers-from-0-to-99-if-I-took-a-random-element-out-then-how-would-you-find-that-which-one-I-took-out-How-would-you-solve-this-if-1-The-array-is-sorted-or-2-The-array-is-not-sorted

https://stackoverflow.com/questions/22826953/how-to-create-array-of-100-with-integers-from-1-1000

https://jsperf.com/fast-array-foreach

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Uint8Array

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint8Array

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint32Array

https://en.wikipedia.org/wiki/Bit_array

https://stackoverflow.com/questions/29523206/how-do-i-write-an-8-bit-array-to-a-16-bit-array-of-1-2-size

https://stackoverflow.com/questions/33793246/c-converting-8-bit-values-into-16-bit-values

Typed Arrays

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Typed_arrays

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint8Array

new_arr = new Uint8Array(100); // new in ES2017

// Uint8Array(100) [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]

old_arr = new Array(100);
// (100) [empty × 100]

no for & create Array 100

new Uint8Array(100).map((item, i) => (item = i));

// Uint8Array(100) [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99]

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bitwise-operators

不用加减乘除运算符, 求整数的7倍

"use strict";

/**
 *
 * @author xgqfrms
 * @license MIT
 * @copyright xgqfrms
 * @created 2019-08-15
 *
 * @description bitwise-operators
 * @description 不用加减乘除运算符, 求整数的7倍
 * @description 7 times, without multiplication
 * @augments
 * @example
 * @link https://www.cnblogs.com/xgqfrms/p/11355923.html
 *
 */

let log = console.log;

// 7 times, without multiplication
const autoSeventTimes = (num = 0, times = 7) => {
    num = Math.abs(num);
    let x = Math.floor(times / 2);
    return (num << x) - num;
};

let xyz = autoSeventTimes(3);
// 21

console.log(`xyz =`, xyz);

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https://hiluluke.cn/

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