JS中实现数组开头添加元素

//向数组开头添加一个或多个元素，并返回新的长度，该方法改变原数组
let person= ['张三', '李四', '王五'];
console.log(person.unshift('小明')); // 4
console.log(person); // ["小明", "张三", "李四", "王五"]

var arr1 = ['张三', '李四', '王五'];
var arr2 = ['小明', ...arr1];
console.log(arr2); // ["小明", "张三", "李四", "王五"]

//用于连接两个或多个数组，并返回一个新数组，该方法不会改变原数组
var arr3 = ['aaa'];
console.log(arr3.concat(arr2)); // ["aaa", "小明", "张三", "李四", "王五"]
console.log(arr2); // ["小明", "张三", "李四", "王五"]

function prepend(arr, item) {
    var newarr = arr.concat();
    newarr.unshift(item)
    return newarr
}
var arr = [1, 2, 3, 4];
var item = 10

function prepend(arr, item) {
    var newarr = arr.slice();
    newarr.unshift(item)
    return newarr
}
var arr = [1, 2, 3, 4];
var item = 10;

function prepend(arr, item) {
    return [item].concat(arr)
}
var arr = [1, 2, 3, 4];
var item = 10;

function prepend(arr, item) {
    var newarr = [item];
    newarr.push.apply(newarr,arr)
    return newarr
}
var arr = [1, 2, 3, 4];
var item = 10;

function prepend(arr, item) {
    var newarr = arr.slice();
    newarr.splice(0,0,item);
    return newarr
}
var arr = [1, 2, 3, 4];
var item = 10;

function prepend(arr, item) {
    var newarr = [item];
    for(var i = 0; i < arr.length; i++){
        newarr.push(arr[i])
    }
    return newarr
}
var arr = [1, 2, 3, 4];
var item = 10;