array.html

<!DOCTYPE html>
<html>
<head>

</head>
<body>
<h1>JS Array</h1>
<p>unshift()</p>
<button id="button" onclick="arr()">try it</button>
<p id="demo"></p>

    
<script>
var fruits = ["Banana", "Orange", "Apple", "Mango"];
document.getElementById("demo").innerHTML = fruits;
    
    
function arr(){
    console.log(contains(fruits, "Lemon"));
    if (contains(fruits, "Lemon") == false){
        fruits.unshift("Lemon");
    } 
    console.log(contains(fruits, "Lemon"));
    document.getElementById("demo").innerHTML = fruits;
}

function contains(arr, element){
    for (i in arr){
        if (arr[i] == element){
            return true;
        }
    }
    return false;
}
    
    
    
//arr = ["a", "b", "c", "d", "e"];
//for (i in arr){
//    console.log(arr[i]);
//}
    
//验证while(0)是否会执行: 不会
//学到： len--是先执行再减一
//var len = 5;
//while(len--){
//    console.log(len);
//}
    
//while(0){
//    console.log("heelow");
//}
    

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