누구나 알고 있는 JavaScript 정규식에 대한 자세한 설명

var pattern = /hello/ig;

var s = 'you love me and I love you';
var pattern = /you/;
var ans = pattern.test(s);
console.log(ans); // true

var s = 'you love me and I love you';
var pattern = /you/;
var ans = pattern.exec(s);
console.log(ans); // ["you", index: 0, input: "you love me and I love you"]
console.log(ans.index); // 0
console.log(ans.input); // you love me and I love you

var s = 'you love me and I love you';
var pattern = /y(o?)u/;
var ans = pattern.exec(s);
console.log(ans);   // ["you", "o", index: 0, input: "you love me and I love you"]
console.log(ans.length) // 2

var s = 'you love me and I love you';
var pattern = /you/;
var ans = s.search(pattern);
console.log(ans);  // 0

var s = 'you love me and I love you';
console.log(s.match(/you/));    // ["you", index: 0, input: "you love me and I love you"]
console.log(s.match(/you/g));   // ["you", "you"]

var s = 'you love me and I love you';
console.log(s.replace('you', 'zichi')); // zichi love me and I love you
console.log(s.replace(/you/, 'zichi')); // zichi love me and I love you
console.log(s.replace(/you/g, 'zichi'));    // zichi love me and I love zichi

var s = 'I love you';
var pattern = /love/;
var ans = s.replace(pattern, '$`' + '$&' + "$'");
console.log(ans); // I I love you you

var s = 'I love you';
var pattern = /love/;
var ans = s.replace(pattern, function(a) {　　// 只有一个参数，默认为匹配到的串（如还有参数，则按序表示子表达式和其他两个参数）
  return a.toUpperCase();
});
console.log(ans); // I LOVE you

var s = 'you love me and I love you';
var pattern = 'and';
var ans = s.split(pattern);
console.log(ans);   // ["you love me ", " I love you"]

var s = 'you love me and I love you';
var pattern = /and/;
var ans = s.split(pattern, 1);
console.log(ans);   // ["you love me "]

var s = 'hello world welcome to my world';
var pattern = /hello.*world/;
var ans = pattern.exec(s);
console.log(ans)  // ["hello world welcome to my world", index: 0, input: "hello world welcome to my world"]

var s = 'hello world welcome to my world';
var pattern = /hello.*?world/;
var ans = pattern.exec(s);
console.log(ans)  // ["hello world", index: 0, input: "hello world welcome to my world"]

var s = 'hello world';
var pattern = /(hello)/;
var ans = pattern.exec(s);
console.log(ans);

var s = 'hello world';
var pattern = /(h(e)llo)/;
var ans = pattern.exec(s);
console.log(ans); // ["hello", "hello", "e", index: 0, input: "hello world"]

var s = 'hello world';
var pattern = /(h\w*o)\s*(w\w*d)/;
var ans = s.replace(pattern, '$2 $1')
console.log(ans); // world hello

var s = 'hellohellochinaworldworld';
var pattern = /(\w+)\1/g;
var a = s.match(pattern);
console.log(a); // ["hellohello", "worldworld"]

var s = 'hellohellochinaworldworld';
var pattern = /(\w+)\1/g;
var ans;
do {
　　ans = pattern.exec(s);
　　console.log(ans);
} while(ans !== null);

// result
// ["hellohello", "hello", index: 0, input: "hellohellochinaworldworld"] index.html:69
// ["worldworld", "world", index: 15, input: "hellohellochinaworldworld"] index.html:69
// null

var s = 'hellohellochinaworldworld';
var pattern = /(\w+)\1/g;
var ans = [];
s.replace(pattern, function(a, b) {
　ans.push(b);
});
console.log(ans);   // ["hello", "world"]

String.prototype.getMost = function() {
  var a = this.split('');
  a.sort();
  var s = a.join('');
  var pattern = /(\w)\1*/g;
  var a = s.match(pattern);
  a.sort(function(a, b) {
    return a.length < b.length;
  });
  var letter = a[0][0];
  var num = a[0].length;
  return letter + &#39;: &#39; + num;
}

var s = &#39;aaabbbcccaaabbbcccccc&#39;;
console.log(s.getMost()); // c: 9

// 获取字符串中以ing结尾的单词的前半部分
var s = 'I love dancing but he likes singing';
var pattern = /\b\w+(?=ing\b)/g;
var ans = s.match(pattern);
console.log(ans); // ["danc", "sing"]

// 获取第五位不是i的单词的前四位
var s = 'I love dancing but he likes singing';
var pattern = /\b\w{4}(?!i)/g;
var ans = s.match(pattern);
console.log(ans); // ["love", "like"]

var s = 'http://www.cnblogs.com/zichi/';
var pattern = /http:\/\/www\.cnblogs\.com\/zichi\//;
var ans = pattern.exec(s);
console.log(ans); // ["http://www.cnblogs.com/zichi/", index: 0, input: "http://www.cnblogs.com/zichi/"]

var s = "I don't like you but I love you";
var pattern = /I.*(like|love).*you/g;
var ans = s.match(pattern);
console.log(ans); // ["I don't like you but I love you"]

var s = "I don't like you but I love you";
var pattern = /I.*?(like|love).*?you/g;
var ans = s.match(pattern);
console.log(ans); // ["I don't like you", "I love you"]

String.prototype.trim = function() {
  return this.replace(/(^\s*)|(\s*$)/g, "");
};
var s = '    hello  world     ';
var ans = s.trim();
console.log(ans.length);    // 12

String.prototype.getAns = function() {
  var pattern = /(?=((?!\b)\d{3})+$)/g;
  return this.replace(pattern, ',');
}

var s = '123456789';
console.log(s.getAns());  // 123,456,789

String.prototype.getMost = function() {
  var a = this.split('');
  a.sort();
  var s = a.join('');
  var pattern = /(\w)\1*/g;
  var a = s.match(pattern);
  a.sort(function(a, b) {
    return a.length < b.length;
  });
  var letter = a[0][0];
  var num = a[0].length;
  return letter + &#39;: &#39; + num;
}

var s = &#39;aaabbbcccaaabbbcccccc&#39;;
console.log(s.getMost()); // c: 9