javascript - 或者 Regex 的交替返回比它应该的更多的结果？

Question

代码修改自https://www.w3schools.com/jsref/tryit.asp?filename=tryjsref_regexp_xy .

<p>Click the button to do a global search for any of the specified alternatives (red|green).</p>

<button onclick="myFunction()">Try it</button>

<p id="demo"></p>

<script>
  function myFunction() {
    var str = "re, green, red, green, gren, gr, blue, yellow";
    var patt1 = /(blue|red)/;
    var result = str.match(patt1);
    document.getElementById("demo").innerHTML = result;
  }
</script>

结果是red,red。但是，只有一个 red。为什么返回两个？

Answer 1

因为您在正则表达式中使用了组，所以 match 会返回匹配的字符串和组(因此包含两个相同元素的数组)。使用 /blue|red/g 代替(g 使得 match 将在 findig 第一次匹配后继续搜索)

function myFunction() {
  var str = "re, green, red, green, gren, gr, blue, yellow";
  var patt1 = /blue|red/g;
  var result = str.match(patt1);
  demo.innerHTML = result;
}

<p>Click the button to do a global search for any of the specified alternatives (red|green).</p>

<button onclick="myFunction()">Try it</button>

<p id="demo"></p>