JS JavaScript how to get the subscript of a value in the array

js The subscript of a value in the array
javascript Know the value of an element in an array , How to get array subscripts
JS Get the subscript of an element of the array Function method

use prototype Prototype implementation , Find the index value of the element in the array
js Find the position of the element in the array （index value ）
Traverse all arrays , When the value in the array is the same as the value you expect, just return the subscript .

/*
*  Get the subscript of an element 
* arr:  The array passed in 
* obj:  The element that needs to get the subscript 
* */
function getArrayIndex(arr, obj) {
    var i = arr.length;
    while (i--) {
        if (arr[i] === obj) {
            return i;
        }
    }
    return -1;
}

// use prototype Prototype implementation , Find the index value of the element in the array 
Array.prototype.getArrayIndex=function(obj){
 for(var i=0;i<this.length;i++){
  if(this[i]===obj){
   return i;
     }
 }
    return -1;
}
var testarr = [1,2,3,4,5];
// obtain 2 stay testarr The subscript in is 1
testarr.getArrayIndex(2);
    

     
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// Method to get the next subscript index of an element 
var obj = 2;
var arrlist = [1,2,3,4,5];
var index = getArrayIndex(arrlist,obj);
var to = index+1;
    if(to > arrlist.length){
        to = arrlist.length-1;
    }
    

     
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Expanding knowledge ：
1, What is an array
An array is an ordered collection of values , Each value is called an element , And each element has a position in the array , In numbers , Known as the index .\
js The array of is typeless , Array elements can be of any type , Different elements in the same array may be objects or arrays .
The indexes of array elements do not have to be continuous , There can be gaps between elements , It's called a sparse array .
For example, sparse arrays var c = [1,,2]; The maximum index is 2, The array length is 3.
Each array has a length attribute . For non sparse arrays ,length Property is the number of array elements ,
For sparse arrays , Elemental length Attribute is larger than the index of all elements .