<script text="text/javascript">
　　var txt = 'Hello World!'
　　var reg = new RegExp('hello', 'i');
　　if(reg.test(txt)) {
　　　　console.log(txt.match(reg));
　　}
</script>

<script text="text/javascript">
  var txt = 'This is just a test.'
  var reg = new RegExp('is', 'g');//区分大小写
  var reg01 = new RegExp('is', 'gi');//不区分大小写
  if(reg.test(txt)) {
    console.log(txt.match(reg));//["is", "is"]
    console.log(txt.match(reg).length);//2
  }
</script>

<script type="text/javascript">
  //以下代码不能够匹配字符串"an"，尽管"an"后面已经换行了，但"an"并不是字符串行的结尾。
  var txt1 = 'This is an\n apple'; 
  var reg1 = /an$/;
  console.log(txt1.match(reg1));//null
  //以下代码能够匹配到字符串"an"
  var txt2 = 'This is an\n apple';
  var reg2 = /an$/m;
  console.log(txt2.match(reg2));//["an", index: 8, input: "This is an↵ apple"]  
  //以下是多行匹配开头示例
  var txt3 = 'This is an\n apple';
  var reg3 = /^\sapp/;
  console.log(txt3.match(reg3));//null
  
  var txt4 = 'This is an\n apple';
  var reg4 = /^\sapp/m;// /^ app/m
  console.log(txt4.match(reg4));//[" app", index: 11, input: "This is an↵ apple"]
</script>

<script type="text/javascript">
  var txt4 = 'This is an\n apple';
  var reg4 = new RegExp('^\\sapp', 'm');
  console.log(txt4.match(reg4));//[" app", index: 11, input: "This is an↵ apple"]
</script>

<script type="text/javascript">
  var txt = 'This is just a test';
  var reg = new RegExp('st', 'g');
  if(reg.global) {
    console.log(txt.match(reg));//["st", "st"]
  }
</script>

<script type="text/javascript">
  var txt = 'If you love code, you should code everyday.';
  var reg = new RegExp('ou', 'g');
  var length = txt.match(reg).length;
  for(var i = 0; i < length; i++) {
    reg.test(txt);
    console.log(reg.lastIndex);
  }
</script>

<script>
  var reg1 = new RegExp('yoho', 'm');
  var reg2 = new RegExp('\\w');
  var reg3 = /\w/m;
  console.log(reg1.source);//yoho
  console.log(reg2.source);//\w
  console.log(reg3.source);//\w
</script>

<script>
  var reg = new RegExp('ou', 'g');
  reg = /\w/;
</script>

<script>
  var txt = 'If you love code, you should code everyday.';
  var reg = new RegExp('ou', 'g');
  var length = txt.match(reg).length;
  for(var i = 0; i < length; i++) {
    console.log(reg.exec(txt));
  }
</script>

<script>
  var txt = 'I code everyday.';
  var reg = new RegExp('code');
  console.log(reg.test(txt));//true
</script>