Locate a value in a given array

method 1

var arr = [20,10,33, 14, 16];
var item = 16;
function choose(arr, item){
    for(var i = 0; i < arr.length; i++){
        if(arr[i] == item) return i;
    }
    return -1;
}

var end = choose(arr, item);
console.log(end);

var arr = [20,10,33,14, 16];
var item = 13;

　

Method 2 reduce method

var arr = [20,10,33,14, 16];
var item = 13;

function choose(arr, item){
    var back = -1;
    var i = 0;
    arr.reduce((newarr, one)=>{
        if(one == item){
            back = i;
        }
        i = i + 1;
    },[]);
    return back;
}

 

Method 3

var end = choose(arr, item);
console.log(end);


var arr = [20,10,33,14, 16];
var item = 16;

function indexOf(arr, item){
    return arr.indexOf(item);
}
var end = indexOf(arr, item);
console.log(end);

　　

Method 4

var arr = [20,10,33,14, 16];
var item = 16;

function choose(arr, item){
    if(Array.prototype.indexOf){
        return arr.indexOf(item);
    }
    else{
        for(var i = 0; i < arr.length; i++){
            if(arr[i] == item) return i;
        }
        return -1;
    }
}

var end = choose(arr, item);
console.log(end);

 

Method 4 1 and 3 are mixed, but with an array method of determining whether it has indexOf, Array configuration whether it has prototyping indexOf