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HTML

              
                <textarea id='cont'></textarea>

<p><input type="button" value="匹配hi" onclick="t1();"></p>
<p><input type="button" value="正匹配单词hi" onclick="t2();"></p>
<p><input type="button" value="匹配hi开头的单词但不是hi" onclick="t3();"></p>
              
            
!

CSS

              
                		textarea{
			width: 400px;
			height: 200px; 
		}
              
            
!

JS

              
                function t1(){
  var cont = document.getElementById('cont');
  var cv = cont.value;
  var reg = /hi/;//仅仅是看字符串中有没有hi
  alert(reg.test(cv));//满足 返回true  不满足 返回false
}
function t2(){
  var cont = document.getElementById('cont');
  var cv = cont.value;
  var reg = /\bhi\b/;//正则测试单词hi
  alert(reg.test(cv));//满足 返回true  不满足 返回false
}
function t3(){
  var cont = document.getElementById('cont');
  var cv = cont.value;
  var reg = /\bhi\b/;//正则测试hi开头的单词但不是hi
  alert(reg.test(cv));//满足 返回true  不满足 返回false
} 
              
            
!
999px

Console