returning index of array in js code example

Example 1: index of value in array

// for dictionary case use findIndex 
var imageList = [
   {value: 100},
   {value: 200},
   {value: 300},
   {value: 400},
   {value: 500}
];
var index = imageList.findIndex(img => img.value === 200);

Example 2: get the index of object in array

var elementPos = array.map(function(x) {return x.id; }).indexOf(idYourAreLookingFor);
var objectFound = array[elementPos];