编辑代码

function swapArr(arr, index1, index2) {
    arr[index1] = arr.splice(index2, 1, arr[index1])[0];
    return arr;
}
function toFirst(fieldData,index) {
    if(index!=0){
        // fieldData[index] = fieldData.splice(0, 1, fieldData[index])[0]; 这种方法是与另一个元素交换了位子，
        fieldData.unshift(fieldData.splice(index , 1)[0]);
    }
}
function upGo(fieldData,index){
    if(index!=0){
        fieldData[index] = fieldData.splice(index-1, 1, fieldData[index])[0];
    }else{
        fieldData.push(fieldData.shift());
    }
}
function downGo(fieldData,index) {
    if(index!=fieldData.length-1){
        fieldData[index] = fieldData.splice(index+1, 1, fieldData[index])[0];
    }else{
        fieldData.unshift( fieldData.splice(index,1)[0]);
    }
}
let a = ['a','b','c','d']
upGo(a,1)
downGo(a,2)
console.log(a)