Judging that all are equal is equivalent to judging that one of them is not equal,

function isAllEqual(array){
    if(array.length>0){
       return !array.some(function(value,index){
         return value !== array[0];
       });   
    }else{
        return true;
    }
}

The questioner did not say it is a simple array; if the array elements include Object, etc., then the above answer will basically fail. Then the problem actually becomes how to judge that two Objects are equal, and then it involves recursion... In short, it is not that simple, so I won’t go into details about the claw machine code.

function compare(array1, array2) 
{
(array1.length == array2.length) && array1.every(function(element, index) {
    return element === array2[index]; 
})
}

function test (arr) {
    return arr.reduce((o, item) => (o.result = o.result && item === o.prev, o.prev = item, o), { result: true, prev: arr[0] }).result
}

Isn’t this something that can be solved with just one cycle?

var equals=function(arr){
             var bool=true;
             for(var i=1,len=arr.length;i<len;i++){
                 if(arr[i]!==arr[0]){bool=false}
             }
             return bool
         }

If you want to consider objects, you can refer to Lodash’s isEqual

Only simple types are considered:

var arr = [/*elements*/];

var isAllEqual = new Set(arr).size === 1;

How about I show off my wits?