4.1 for of遍历
4.2 模板字符串
4.3 新增方法
4.3.1 String.includes()
4.3.2 String.startsWith()
4.3.3 String.endsWith()
4.3.4 String.repeat()
4.3.5 String.padStart()
4.3.6 String.padEnd()
4.3.7 String.trimStart()
4.3.8 String.trimEnd()
