Using the JavaScript REST API Client: comparison of v.8 v...

var capi,
    credentials = {
        login: 'admin',
        password: 'publish',
    };

capi = new eZ.CAPI(
    'http://example.com',
    new eZ.BasicAuthAgentHttpBasicAuthAgent(credentials)
);
capi.logIn(function (error, response) {
    if ( error ) {
        console.log('Error!');
        return;
    }
    console.log("The credentials are valid");
});