How to splice an element to the start of an array?

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How can I add new array elements at the beginning of an array in JavaScript? 6 answers

JavaScript Array rotate() 16 answers

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尝试在for循环中移动数组：

function rotate(arr, num){
    for(var i = 0; i < num; i++){
        item = arr[arr.length-1]
        arr.splice(arr.length-1, 1);
        arr.unshift(item)
    }
    return arr
}

alert(JSON.stringify(rotate(["Harry", "Sarah", "Oscar", "Tina"], 2)));
alert(JSON.stringify(rotate(["Harry", "Sarah", "Oscar", "Tina"], 1)));

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You don't need a loop. First splice the last num elements off the end of the array, then splice them all onto the front.

function rotate(arr, num) {
        var lastN = arr.splice(-num, num);
        [].splice.apply(arr, [0, 0].concat(lastN));
        return arr;
    }
document.getElementById("result").innerHTML = JSON.stringify(rotate(["Harry", "Sarah", "Oscar", "Tina"], 2));

<div id="result"></div>

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