12-给元素查索引

<!DOCTYPE html>
<html>
<head lang="en">
    <meta charset="UTF-8">
    <title></title>
</head>
<body>
<script>

    var arr = ["a","b","c","d","c","b","a"];

    //indexOf从前往后给元素查索引，找到一个后，立刻返回。
    console.log(arr.indexOf("a"));
    console.log(arr.indexOf("b"));
    console.log(arr.indexOf("x"));

    //lastIndexOf从后往前给元素查索引，找到一个后，立刻返回。
    console.log(arr.lastIndexOf("a"));
    console.log(arr.lastIndexOf("b"));
    console.log(arr.lastIndexOf("x"));




</script>
</body>
</html>

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