es6字符串拓展

1. 字符串可以直接遍历啦

   for(let codepoint of 'foo'){
       console.log(codepoint); // f,o,o
   }
   

2. includes(), startsWidth(), endsWidth()

   const s='hello world';
   s.startWidth('hello') // true
   s.endsWidth('d') // true
   s.includes('o')  // true
   s.includes('1')  // false
   

3. repeat

   'x'.repeat(3) // xxx
   

4. 模板字符串

   let name="bob", time ="today";
   console.log(`hello ${name}, how are you${time}`)