JavaScript——正则 字符边界

<input type="text" name="user">
<div id="flag"></div>

<script>
let str = 'abhja23498kjgj';
let str2 = '345fgd33';
let str3 = '3657dfg65jh6767';
console.log(/^\d/.test(str));//false   ^开始边界  $结束边界
console.log(/^\d/.test(str2));//true  
console.log(/^\d+\w+$/.test(str3));

document.querySelector("[name='user']").addEventListener('keyup',function(){
  // console.log(this.value);
  // console.log(this.value.match(/[a-z]{3,6}/));//会匹配除无数个3-6的字符串，并没有真正限制从开头到结尾的3-6位长度
  // console.log(this.value.match(/^[a-z]{3,6}$/));//整个字符串3-6位
  let flag = this.value.match(/^[a-z]{3,6}$/)
  document.getElementById('flag').innerHTML = flag ? '符合' : '不符合'
})
</script>