面试官：说说你对正则表达式的理解？应用场景？ #

const re = /\d+/g;

const re = new RegExp("\\d+","g");

const rul = "\\d+"
const re1 = new RegExp(rul,"g");

var re = /pattern/flags;
var re = new RegExp("pattern", "flags");

const reg = /ab{1,3}c/

const string = "12345";
const regx = /(\d{1,3})(\d{1,3})/;
console.log( string.match(reg) );
// => ["12345", "123", "45", index: 0, input: "12345"]

var string = "12345";
var regex = /(\d{1,3}?)(\d{1,3})/;
console.log( string.match(regex) );
// => ["1234", "1", "234", index: 0, input: "12345"]

let str = "John Smith";

// 交换名字和姓氏
console.log(str.replace(/(john) (smith)/i, '$2, $1')) // Smith, John

let str = "I love JavaScript";

let result = str.match(/Java(Script)/);

console.log( result[0] );     // JavaScript（完全匹配）
console.log( result[1] );     // Script（第一个分组）
console.log( result.length ); // 2

// 其他信息：
console.log( result.index );  // 7（匹配位置）
console.log( result.input );  // I love JavaScript（源字符串）

let str = "I love JavaScript";

let result = str.match(/Java(Script)/g);

console.log( result[0] ); // JavaScript
console.log( result.length ); // 1

let str = "I love JavaScript";

let result = str.match(/HTML/);

console.log(result); // null

const regexp = /t(e)(st(\d?))/g;
const str = 'test1test2';

const array = [...str.matchAll(regexp)];

console.log(array[0]);
// expected output: Array ["test1", "e", "st1", "1"]

console.log(array[1]);
// expected output: Array ["test2", "e", "st2", "2"]

let str = "A drop of ink may make a million think";

console.log( str.search( /ink/i ) ); // 10（第一个匹配位置）

const reg1=/javascript/i;
const reg2=/javascript/ig;
console.log('hello Javascript Javascript Javascript'.replace(reg1,'js'));
//hello js Javascript Javascript
console.log('hello Javascript Javascript Javascript'.replace(reg2,'js'));
//hello js js js

console.log('12, 34, 56'.split(/,\s*/)) // 数组 ['12', '34', '56']

let str = 'More about JavaScript at https://javascript.info';
let regexp = /javascript/ig;

let result;

while (result = regexp.exec(str)) {
  console.log( `Found ${result[0]} at position ${result.index}` );
  // Found JavaScript at position 11
  // Found javascript at position 33
}

let str = "I love JavaScript";

// 这两个测试相同
console.log( /love/i.test(str) ); // true

const reg = /^[1-9][0-9]{4,14}$/
const isvalid = patrn.exec(s)

var patrn=/^[a-zA-Z]{1}([a-zA-Z0-9]|[._]){4,19}$/;
const isvalid = patrn.exec(s)

const protocol = '(?<protocol>https?:)';
const host = '(?<host>(?<hostname>[^/#?:]+)(?::(?<port>\\d+))?)';
const path = '(?<pathname>(?:\\/[^/#?]+)*\\/?)';
const search = '(?<search>(?:\\?[^#]*)?)';
const hash = '(?<hash>(?:#.*)?)';
const reg = new RegExp(`^${protocol}\/\/${host}${path}${search}${hash}$`);
function execURL(url){
    const result = reg.exec(url);
    if(result){
        result.groups.port = result.groups.port || '';
        return result.groups;
    }
    return {
        protocol:'',host:'',hostname:'',port:'',
        pathname:'',search:'',hash:'',
    };
}

console.log(execURL('https://localhost:8080/?a=b#xxxx'));
protocol: "https:"
host: "localhost:8080"
hostname: "localhost"
port: "8080"
pathname: "/"
search: "?a=b"
hash: "#xxxx"

function execUrlParams(str){
    str = str.replace(/^[#?&]/,'');
    const result = {};
    if(!str){ //如果正则可能配到空字符串，极有可能造成死循环，判断很重要
        return result; 
    }
    const reg = /(?:^|&)([^&=]*)=?([^&]*?)(?=&|$)/y
    let exec = reg.exec(str);
    while(exec){
        result[exec[1]] = exec[2];
        exec = reg.exec(str);
    }
    return result;
}
console.log(execUrlParams('#'));// {}
console.log(execUrlParams('##'));//{'#':''}
console.log(execUrlParams('?q=3606&src=srp')); //{q: "3606", src: "srp"}
console.log(execUrlParams('test=a=b=c&&==&a='));//{test: "a=b=c", "": "=", a: ""}