How to update contact email with JavaScript API?
There are many ways you can update email for contact


Using Email api with create action

CRM.api3('Email', 'create', {"email": "aaa@asas.comsdsd",  "id": 201}).done(function(result) { // do something});

Using Email api with replace action



  CRM.api3('Email', 'replace', {
      "values": {"0":{"email":"asasa@asas.com","location_typ_id":"Home"}},
      "contact_id": 203
    }).done(function(result) {
      // do something
    });




Using Contact api with Email chain api



CRM.api3('Contact', 'create', {
  "id": 203,
  "api.Email.replace": {"values":{"0":{"email":"assdfsfdsasa@asas.com","location_typ_id":"Home"}}}
}).done(function(result) {
  // do something
});



HTH

Pradeep