1、数组去重

Array.prototype.DuplicateRemoval = function(){    let res = [this[0]];    for(let i = 1; i < this.length; i++){        var repeat = false;        for(let j = 0; j < res.length; j++){            if(this[i] == res[j]){                repeat = true;                break;            }        }        if(!repeat){            res.push(this[i]);        }    } return res;}var arr = [1, '1', '1', 'b', 'd', 'e', 'e', 1, 0]console.log(arr.DuplicateRemoval());

 2、页面刷新前触发

window.addEventListener("beforeunload", function(event) {  event.returnValue = "You may have unsaved Data";});