what's index in array 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: how do i index into array

>>> x = np.arange(10)
>>> x[2]
2
>>> x[-2]
8