using key with js code example

Example 1: get keys objet javascript

var foo = {
  'alpha': 'puffin',
  'beta': 'beagle'
};

var keys = Object.keys(foo);
console.log(keys) // ['alpha', 'beta'] 
// (or maybe some other order, keys are unordered).

Example 2: js key in dict

"key" in obj // true, regardless of the actual value

Example 3: js variable for key obj

{
    [yourKeyVariable]: someValueArray,
}