360 Front-end Star Project-Creation and use of regular expressions (Wang Feng)

1. The creation and use of regular expressions

1.1 Create regular expressions

• Use regular expression literals to
  const reg = /[a-z]\d+[a-z]/i;
/ /include the content of regular expressions, [a-z]letters, \dnumbers, and the +preceding ( \d) repeated one or more times, to iindicate modifiers, regular expressions ignore case

  • Advantages: simple and convenient and no need to consider secondary escaping
  • Disadvantages: Sub-content cannot be reused, too long regularity leads to poor readability

• Use RegExp constructor

  const alphabet = '[a-z]';
  const reg = new RegExp(`${alphabet}\\d+${alphabet}`, 'i');
  

  • Advantages: Sub-content can be reused, and readability can be improved by controlling the granularity of sub-content
  • Disadvantages: The problem of secondary escaping is very easy to cause bugs

    const reg = new RegExp(`\d+`);
    reg.test('1'); // false
    reg.test('ddd'); // true
    

1.2 Use regular expressions

• RegExp.prototype.test()

  const reg = /[a-z]\d+[a-z]/i;
  reg.test('a1a'); // true
  reg.test('1a1'); // false
  reg.test(Symbol('a1a')); // TypeError
  

  Input: The input string is required. If the input is not a string type, the type conversion will be attempted. If the conversion fails, a TypeError will be
  output: true or false, indicating that the match is successful or failed

• RegExp.prototype.source (content) and RegExp.prototype.flags (modifiers and sort them in ascending order)

  const reg = /[a-z]\d+[a-z]/ig;
  reg.source; // "[a-z]\d+[a-z]"
  reg.flags; // "gi"
  

• RegExp.prototype.exec() 和 String.prototype.match()

  const reg = /[a-z]\d+[a-z]/i;
  reg.exec('a1a'); // ["a1a", index: 0, input: "a1a", groups: undefined]
  reg.exec('1a1'); // null
  'a1a'.match(reg); // ["a1a", index: 0, input: "a1a", groups: undefined]
  '1a1'.match(reg); // null
  

  Input: RegExp.prototype.exec requires input of a string, and will try to convert when it encounters a non-string type;
  String.prototype.match requires input of a regular expression, if it encounters other types, it will first try to convert to a string, and then use the string as source creates regular expressions

  Output: match success, return match result, match failure, return null

Since the data format returned by String.prototype.match is not fixed, it is recommended to use RegExp.prototype.exec in most cases

• RegExp.prototype.lastIndex
  Note: lastIndex will not reset by itself, only reset to 0 when the last match fails, so when you need to use the same regular expression repeatedly, please match new characters every time Reset lastIndex before the string!
• String.prototype.replace()、String.prototype.search()、String.prototype.split()

2. Three application scenarios

2.1 Scenario 1: Regular and numerical

Numerical judgment process:

• /[0-9]+/ : Incomplete match (as long as it contains numbers)
• /^\d+$/: Cannot match signed values ​​and decimals
• /^[+-]?\d+(\.\d+)?$/: Cannot match decimals without integral part (.123)
• /^[+-]?(?:\d*\.)?\d+$/: Cannot match the value with no decimal part (2.) and scientific notation (-2.e + 4)

Complete numerical regularity:

• /^[+-]?(?:\d+\.?|\d*\.\d+)(?: e[+-]?\d+)?$/i

Use regularization to process values:

• Numerical analysis

  const reg = const reg = /[+-]?(?:\d*\.)?\d+(?:e[+-]?\d+)?(?=px|\s|$)/gi;
  
  function execNumberList(str) {
      reg.lastIndex = 0;
      let exec = reg.exec(str);
      const result = [];
      while (exec) {
          result.push(parseFloat(exec[0]));
          exec = reg.exec(str);
      }
      return result;
  }
  
  console.log(execNumberList('1.0px .2px -3px +4e1px')); // [1, 0.2, -3, 40]
  console.log(execNumberList('+1.0px -0.2px 3e-1px')); // [1, -0.2, 0.3]
  console.log(execNumberList('1px 0')); // [1, 0]
  console.log(execNumberList('-1e+1px')); // [-10]
  

• Value to currency format: that is, a comma is added to every thousandth

  const reg = /(\d)(?=(\d{3})+(,|$))/g;
  function formatCurrency(str) {
     return str.replace(reg, '$1,');
  }
  
  console.log(formatCurrency('1')); // 1
  console.log(formatCurrency('123')); // 123
  console.log(formatCurrency('12345678')); // 12,345,678
  

2.2 Scene two: regularity and color

How many ways to represent colors:

• Hexadecimal notation

  color: #rrggbb;
  color: #rgb;
  color: #rrggbbaa;
  color: #rgba;
  

  const hex = '[0-9a-fA-F]';
  const reg = new RegExp(`^(?:#${hex}{6}|#${hex}{8}|#${hex}{3,4})$`);
  

• rgb / rgba notation

  color: rgb(r, g, b);
  color: rgb(r%, g%, b%);
  color: rgba(r, g, b, a);
  color: rgba(r%, g%, b%, a);
  color: rgba(r, g, b, a%);
  color: rgba(r%, g%, b%, a%);
  

  const num = '[+-]?(?:\\d*\\.)?\\d+(?:e[+-]?\\d+)?';
  const comma = '\\s*,\\s*';
  const reg = new RegExp(`rgba?\\(\\s*${num}(%?)(?:${comma}${num}\\1){2}(?:${comma}${num}%?)?\\s*\\)`);
  

• other

  /* hsl & hsla */
  color: hsl(h, s%, l%);
  color: hsla(h, s%, l%, a);
  color: hsla(h, s%, l%, a%);
  
  /* keywords */
  color: red;
  color: blue;
  /* …… */
  

Use regular processing colors:

• Hexadecimal color optimization

  const hex = '[0-9a-z]';
  const hexReg = new RegExp(`^#(?<r>${hex})\\k<r>(?<g>${hex})\\k<g>(?<b>${hex})\\k<b>(?<a>${hex}?)\\k<a>$`, 'i');
  function shortenColor(str) {
      return str.replace(hexReg, '#$<r>$<g>$<b>$<a>');
  }
  
  console.log(shortenColor('#336600')); // '#360'
  console.log(shortenColor('#19b955')); // '#19b955'
  console.log(shortenColor('#33660000')); // '#3600'
  

2.3 Scenario 3: Regular and URL

Parse the URL:

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://www.360.cn'));
console.log(execURL('http://localhost:8080/?#'));
console.log(execURL('https://image.so.com/view?q=360&src=srp#id=9e17bd&sn=0'));
console.log(execURL('this is not a url'));

console.log(execURL('https://www.360.cn'));
{
  protocol: 'http:',
  host: 'www.360.cn',
  hostname: 'www.360.cn',
  port: '',
  pathname: '',
  search: '',
  hash: ''
}
console.log(execURL('http://localhost:8080/?#'));
{
  protocol: 'http:',
  host: 'localhost:8080',
  hostname: 'localhost',
  port: '8080',
  pathname: '/',
  search: '?',
  hash: '#'
}
console.log(execURL('https://image.so.com/view?q=360&src=srp#id=9e17bd&sn=0'));
{
  protocol: 'https:',
  host: 'image.so.com',
  hostname: 'image.so.com',
  port: '',
  pathname: '/view',
  search: '?q=360&src=srp',
  hash: '#id=9e17bd&sn=0'
}
console.log(execURL('this is not a url'));
{
  protocol: '',
  host: '',
  hostname: '',
  port: '',
  pathname: '',
  search: '',
  hash: ''
}

Use regular to parse search and hash:

function execUrlParams(str) {
    str = str.replace(/^[#?&]/, '');
    const result = {};
    if (!str) {
        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=360&src=srp')); // { q: '360', src: 'srp' }
console.log(execUrlParams('test=a=b=c&&==&a=')); // { test: 'a=b=c', '': '=', a: '' }

3. Summary

How to use regular expressions?

• Clear demand
• Consider comprehensive
• Repeated testing